Baseline Discharge 49.3% SOC

PREFACE: This article looks at the *charging times & achieved state of charge of an AGM battery in multiple scenarios.

1- 50% SOC to 100% SOC at .2C
2- 50% SOC to 100% SOC at .4C
3- 50% SOC Charged at .2C For Exactly 1 Hour
4- 50% SOC Charged at .4C For Exactly 1 Hour
5- 50% SOC Charged at .2C For Exactly 2 Hours
6- 50% SOC Charged at .4C For Exactly 2 Hours

*DISCLAIMER: This test represents this slightly used AGM and may not be representative of a brand new AGM or a battery with more use and in a worse state of health.

DEFINITIONS:

“C” Rate – .2C & .4C – Also called Point Two C and Point 4C. This is just represents a percentage of Ah capacity in either charging or discharging current. For example .2C = 20% of Ah capacity or 20A for a 100Ah battery and .4C = 40% of Ah capacity or a 40A charge or discharge current for a 100Ah battery.

SOC = State of Charge – SOC is a percentage of charge based on battery Ah capacity.

DOD – Depth of Discharge – Is the depth to which the battery has been discharged. For example 80% DOD is also 20% SOC or 80Ah removed from a 100Ah battery.

Ah Capacity = Ampere Hour Capacity – The total ampere hours a battery can store and deliver at a discharge rate that yields a 20 hour discharge time at 77F before hitting a terminal voltage of 10.5V.

20 Hour Discharge Rate – Also the “20 hour rating”. The discharge current at 77F that will yield a 20 hour run time before hitting 10.5V

How long does it take to charge from 50% SOC to 100% SOC?

I have long known that a higher charge rate, with AGM batteries, does not necessarily translate to *significantly faster charge times from 50% SOC to 100% SOC and thought it would be good to test this and measure the actual differences. For the first part of this test, 50% SOC to 100% SOC, I compared a charge rate of .2C with a charge rate of .4C on the same Lifeline GPL-31T battery.

“*Significantly Faster” – Please understand, & take with a grain of salt, what I am comparing “significantly faster” to. I was once told by a quite vociferant expert on AGM batteries, “expert” defined here as a boat owner who had AGM batteries and whom had read only the glossy marketing materials, (grin) that with his 150A alternator he could recharge his 440Ah bank of AGM batteries from 50% to 100% in less than an hour and a half!  Apparently the marketing departments don’t have prerequisites of chemistry 101, Ohm’s law or physics 101?

While the owner was fully capable of basic math, and actually a nice guy to boot, 1.5 hours times 150A = 225Ah’s, he failed to take into consideration that his .34C 150A alternator could not put out 150A for 1.5 hours and his bank, at anywhere close to .34C, would hit absorption voltage rapidly and begin limiting alternator current. He also failed to include for a declining CAR or what is referred to as the charge acceptance rate. Even if his alternator could run at at a face value of 150A it is simply impossible to return 225Ah’s to that bank in 1.5 hours from 50% SOC. I will repeat this, IMPOSSIBLE!

One can’t really can’t blame this owner for his rather misguided expertise because he had been rather grossly mislead by nearly everyone in the industry on the expected charge times from 50% SOC to 100% SOC with AGM batteries. Suffice it to say it is physically impossible to recharge a 440Ah bank of AGM batteries at 50% SOC to 100% SOC in 1.5 hours with a .34C charge current.

Charge Rate Explained:

0.2C = 20% Charge Rate of the Ah Capacity
0.4C = 40% Charge Rate of the Ah Capacity

In this image we have removed 48.54Ah from the battery which tested at 95.69Ah’s of actual capacity. This leaves the battery at 49.3% SOC or just about 50% SOC.  Voltage was used as the cut-off and 12.100V at 5.25A was the stop point for the discharge testing. Voltage as a cut off , at a known constant load and battery temp, is actually extremely repeatable.

The Test Battery:

The battery used for this testing is a 2015 Lifeline Group 31 AGM Deep Cycle battery. It had been used for approx 5 months as part of a bank on a power boat (trawler type) that cruises Maine and resides on a mooring. Once here in my shop it was cycled to 80% DOD then back to 100% SOC twice. It was then equalized at 15.5V for 4 hours, (Lifeline calls this conditioning). The battery then underwent one 20 hour discharge capacity test and was then cycled to 50% SOC and back to 100% SOC, 3 times and another 20 hour capacity test was run. The average of the two 20 hour capacity tests was used as the baseline Ah capacity. The baseline Ah capacity of this battery was 95.69Ah. Throughout testing the ambient temp of the battery averaged about 75.2F. While not 77F, the 75F temp should not have negatively impacted the testing. The battery has a rated Ah capacity, at 20 hours, of 105Ah. For charge and discharge rates I kept them based on the “as new” capacity rating, just as many boaters would do, to keep the test a bit more “real world“.. The battery is rated at 105Ah so -5.25A was the discharge rate used. The test was set up to try and simulate real world use on cruising boats.

Testing Equipment:

Charging – BK Precision 60A Variable Power Supply W/Dedicated Voltage Sensing
Discharging – Array DC Programmable DC Electronic Load W/Dedicated Voltage Sensing
Temperature – Fluke Infrared
Data Logging – Bogart Engineering Pentametric
Images – iPad Air with intervalometer software taking 1 picture every 2 minutes

2 Minutes – 50% SOC to 100% SOC .4C Charge Test

For the .4C charging test the timer was reset to 12:00 and an image was snapped using an intervalometer at 2 minute increments. At 2 minutes the voltage at a .4C charge rate had already risen to 13.6V.

18 Minutes @ .4C Approaching Absorption Voltage

This image shows the charger almost ready to exit bulk charging and enter absorption charging. If you look closely, on this lab grade power supply, you can see a little red light next to the letters “CC”. This means constant-current or BULK charging.

Bulk Charging is the Most Efficient Charging:

Bulk charging is the most efficient part of the recharging process with efficiencies ranging close to 100% of energy delivered by the charger being usable and stored. For AGM’s I have seen this anywhere from 96% to over 99.5%. Once the charge process switches from constant-current/bulk to constant-voltage/absorption, the charge efficiency continues dropping. In the high 90% SOC range we are converting a lot less of the supplied energy into stored energy. Charge efficiency is not a simply single data point number such as 20% efficient or 10% efficient. The Coulombic efficiency varies through the charge curve and is why getting all lead acid batteries back to 100% SOC, including AGM & GEL, takes a long time.

Bulk & Absorption Terminology Confusion

If you read the highlighted part of the Lifeline Battery Technical Manual you will see that Lifeline correctly understands the difference between BULK and ABSORPTION charging. Many companies, including Balmar and some others, do not correctly understand using the word “BULK”. When a company tells you that “bulk” is a voltage limited stage of charging this is PURE MARKETING BOVINE DUNG. Simply put, bulk=constant-current charging not constant-voltage.

BULK – Bulk Charging is the constant current stage of charging where the charge source is limited only by what it can deliver in current. Bulk charging is not a voltage limited stage of charging despite many companies bastardizing the term bulk for apparent marketing purposes.

ABSORPTION – Absorption, float and equalization are all examples of constant voltage charging stages. Absorption or constant-voltage is where the charge source holds voltage steady, hence the term “constant-voltage”. Once voltage is held steady, or it becomes voltage limited, current begins to decline and the charge efficiency worsens as SOC increases. Float charging is a further reduction in the constant-voltage limit and an equalization voltage would be an increase in the constant-voltage limit of charging.

The charging devices we use on boats are all considered CC > CV charge sources, or constant-current (BULK) then to constant-voltage (ABSORPTION, FLOAT & EQ). Simple stuff really. Please understand that BULK is not a voltage limited stage of charging, despite the marketing guru’s vastly missing the mark on this one…

Kudo’s to the guys at Lifeline Battery for properly understanding the difference between BULK and ABSORPTION. Shame on companies who grossly mislead the consumer and use incorrect lingo to pretend they are getting more than they actually are.. Words mean certain things and when we blur the definitions to sell $hit, it CONFUSES PEOPLE. (grin)

Please remember that bulk is not a voltage limited stage of charging it is constant current.

20 Minutes @ .4C Absorption Voltage Attained

Based on this image, and the data logger, I know the battery attained 14.4V at around 19 minutes. Here at 20 minutes, with the voltage now held steady at 14.4V (green CV/constant-voltage light on) we can see that the charge current has already dropped from 42A to 41.5A or a .5A reduction in accepted charge current into the battery.

If we assume that bulk was 100% efficient, and we will for round numbers, the energy returned to the battery at .4C during bulk charging looks like this:

42A X .32 Hours = 13.44 Ah

If we know the battery had 47.15 Ah left in it, at 49.3% SOC then:

47.15Ah + 13.44Ah = 60.59 Ah stored in the battery

60.59 Ah as a % of 95.69 Ah (tested capacity) = 63.3% SOC

If you’re paying attention this battery, when charged at .4C from 49.3% SOC, stayed in BULK/CC for 19 minutes and entered ABSORPTION/CV charging, where current begins declining, at 63.3% SOC. If you’ve listened to net lore or dock lore for years, as I have, we all know AGM’s “don’t come up to absorption until 80-85%” right? Wrong…. The point at which any battery becomes voltage limited or attains the absorption voltage is entirely dependent upon the charge rate you are feeding it.

This clearly charge rate shows very clearly how charge current affects the SOC transition point from bulk to absorption charging.

1 Hour – .4C Recharge

By 1 hour in, our 42A or .4C charge current has already declined to 19.5A..

2 Hours -.4C Recharge

By two hours of charging, at .4C from 50% SOC, we are down to just 7.3A in current flowing into the battery…

3 Hours – .4C Recharge

Here we are at 3 hours and the accepted charge current is now down to 2.8A.. That last few % takes the longest due to declining CAR.

4 Hours – .4C Recharge

By 4 hours, at .4C, in we’re now down to 1.1A in charge acceptance…

50% SOC to 100% SOC at a .4C Recharge Took 5:30

100% SOC was deemed as 0.525A flowing into the battery at 14.4V per the Lifeline Battery Technical Manual.
At a .4C charge rate it took this fairly healthy, though not perfect, group 31 battery 5:30 to reach 100% SOC from 49.3% SOC.

2 Minutes – .2C Recharge

Beginning of .2C Recharge Test:

For this test 12.100V was also used as the cut off voltage after a full 100% recharge. After a full recharge at 14.4V battery then spent 32 hours at a float voltage of 13.4V. It then had a 24 hour resting period. The battery delivered -48.33Ah or just about where it had on the previous test which ended at -48.54Ah.

As we can see in this image, at 2 minutes, the .2C charge rate only has the battery to 13.1V vs. 13.6V at a .4C charge rate. The voltage is climbing slower in bulk at .2C than it did at .4C. This is to be expected.

1 Hour – .2C Recharge

At 1 hour the battery voltage has only risen to 13.8V at a .2C charge rate. The .4C charge rate had attained 14.4V within 19 minutes.

If this was your alternator it had better be robust enough to deliver its full output for at least 1 hour straight. In this case, as you see next, it is 1:16 minutes before your alterntor would even begin to catch a break. A charge rate of .2C on a 450Ah bank, a pretty typical bank on a coastal cruiser these days, is an alternator that can deliver 90A continuously, even when hot.

1 Hour & 16 Minutes – .2C Recharge Absorption Voltage Attained

At 1:16 the battery finally attained 14.4V and the current had begun dropping.

If we again assume that bulk was 100% efficient, and we will for round numbers, the energy returned to the battery at .2C during bulk charging looks like this:

21A X 1.27 Hours = 26.67 Ah

If we know the battery had 47.36 Ah left in it, at 49.5% SOC then:

47.36Ah + 26.67 Ah = 74.03 Ah stored in the battery

74.03 Ah as a % of 95.69 Ah (tested capacity) = 77.4% SOC

This battery, when charged at .2C from 49.5% SOC, stayed in BULK/CC for 1:16 minutes and entered ABSORPTION/CV charging, where current begins declining, at 77.4% SOC.

Once again this clearly shows how charge current affects the SOC transition point from bulk to absorption charging. At .4C the battery attained absorption voltage at approx 63.3% SOC and at a .2C charge rate it attained absorption voltage at approx 77.4% SOC.  See batteries don’t just automatically attain the absorption point at 80% SOC it all depends upon the available charge current..

2 Hours – .2C Recharge

At 2 hours the charge current is down to 11A..

3 Hours – .2C Recharge

At 3 hours the battery is now accepting just 4.2A.

4 Hours – .2C Recharge

At 4 hours the battery is accepting just 1.6A..

Determining 100% SOC

The key piece when charging your batteries is how to determine when you are at 100% SOC. Some battery manufacturers give “*tail-current” or “*return-amps” in their technical manuals, Lifeline battery is one of them..

*Return-Amps” / “Tail-Current” – This is the amount of current flowing into the battery at ABSORPTION VOLTAGE where one can pretty safely determine 100% SOC.

Using return amps, at absorption voltage, (not float voltage) is usually the easiest method to determine 100% SOC when out cruising. This image is a screen capture of the Lifeline Battery Tech Manual. I have highlighted the important part for net return amps determining 100% SOC.

It is saying; A voltage limit (absorption voltage setting) of 14.3V to 14.4V should be used when the battery temperature is at 77F, this battery was at about 75F. When voltage is steady at 14.3V to 14.4V the battery can be deemed 100% full when charging-current,/tail-current/return-amps declines to 0.5% of Ah capacity.

When 14.4V and 0.525A were attained is when I deemed this battery at 100% SOC. Technically, the battery was only at 95.69Ah so I should have used 0.48A but close enough for this experiment.

What Is Full?

It is important to note that some sources claim a tail-current of 2% @ absorption voltage will yield 100% SOC. Odyssey, Northstar and East Penn/Deka all wanted to see 0.3% @ absorption voltage for the Practical Sailor PSOC testing. Lifeline wanted 0.5% and for Firefly we stopped at 0.5% as well. Over many years of capacity testing hundreds and hundreds of batteries, flooded, GEL and AGM I have yet to see a lead acid battery that could delivers its full storage potential at anything less than 0.75% in tail current at absorption voltage. My best research of antiquated data and materials suggests that 2% @ Absorption voltage originated from the Ah counting industry not from batteries actually being “full”.

Tail-Current is always measured at ABSORPTION VOLTAGE…

Please don’t confuse FLOAT tail current with ABSORPTION tail current. Far too many marine charge sources drop to float prematurely. If you check your tail current at 13.4V and see a 0.5% tail-current, you’re not full…

100% SOC – .2C Recharge

Here we are at 100% SOC at the .2C charge rate and it took 5:42 minutes.

Yes, it took longer to attain 100% SOC (per Lifeline battery tech manual) but that time was only about 12 minutes different with double the charge rate.

Both charge rates on this pretty healthy AGM battery took 5.5+/- hours and I have repeated this test with AGM batteries is worse shape that exceeded 7 hours to attain 100% SOC, likely due to sulfation.

IMPORTANT: Please understand that you will never likely charge this fast with a typical smart charger. Take for example the .4C charge rate. At 19 minutes it hit absorption voltage. Many so called “smart chargers” begin a timer, I call it an egg-timer, once absorption voltage has been attained. If that egg-timer clock started at 19 minutes, and was 2 hours long, the charger would have dropped to a float voltage of 13.4V at 2:19! OUCH!!!! Smart? Hardly! Murderous to your marine batteries? You bet!

Considering it took 5:11 minutes of absorption charging at the .4C charge rate your batteries would likely end up grossly under absorbed, under charged and would not last very long. Once we reduce voltage, eg: dropping to float prematurely, I call this premature-floatulation, we dramatically EXTEND charging time to 100% SOC. In my shop I use adjustable power supplies to avoid dumb so called “smart chargers”. With a fully adjustable power supply I can control when the battery changes from absorption to float and not rely on an egg timer. If I desire a timer cut off I simply program a digital wall timer.

Is too much current bad for an AGM Battery?

For AGM batteries generally speaking the more charge current the better the longevity of the bank. It helps, not hinders, with overall longevity to charge at high rates. Higher charge rates in AGM batteries actually yields longer life not shorter life. Dave V. the lead engineer at Lifeline battery published a study supporting higher charge rates being good for AGM’s a long time ago but it still holds true today.. Odyssey battery, thin plate pure lead AGM batteries, wants to see a minimum of .4C in charge current and Lifeline wants to see a minimum of .2C as recommended charge current.

This is from the conclusion section of Dave V’s study:

“In order to achieve the maximum cycle life from sealed lead acid batteries, (AGM) not only should the DOD be kept as low as possible, but the charge current limit should be as high as possible.”

The study then goes on to suggest that a balance needs to be met between equipment and optimal cycle life. Today Dave suggests a minimum charge current of .2C for Lifeline AGM’s.

It is a pretty rare boat that can muster a .4C charge rate, but some do. On a 450Ah bank that would be an alternator or large inverter/chargers that could sustain 180A when hot. Unless the boat has a massive Electrodyne alternator or multiple stacked “Combis” (inverter/chargers) it is quite rate to see even a 200A continuous charge rate.

You as a boat owner will have to decide what it’s worth in terms of equipment costs to charge your AGM’s at high charge rates. The eternal question of “Do AGM’s charge faster with high charge rates applied?” seems to still be open for debate. This battery only saw an approx 12 minute difference in a 5.5hour charge period but yes it did charge “faster” at .4C than it did at .2C.  Double the charge current to shave 12 minutes? It may be worth it to some, but getting to 100% is not the whole story….

It Is Important To get Back to 100% SOC

The importance of getting back to 100% SOC, as often as possible, can not be over emphasized. Here Lifeline Battery is referring to the “walk down” effect of PSOC use (*partial state of charge cycling). By not recharging to 100%, as often as possible, your Ah capacity will gradually “walk down” as sulfation becomes permanent and ruins them.

SUMMARY: In this portion of the testing 50% to 100% SOC, on this AGM battery, the difference between a .4C and a .2C charge rate, netted a 12 minute total charge time difference.

*For more information on the effects of PSOC cycling AGM batteries please read the May 2015 and August 2015 issues of Practical Sailor Magazine.

BEGIN: .2C – 2 Hour Recharge Then Discharge Test

In this second part of the testing I am replicating a few typical scenarios for recharging on a cruising boat. No one wants to run the engine or generator for very long so I wanted to illustrate what kind of energy can be stored in the AGM battery at a 2 hour time interval at a .2C charge rate.

This test started with a discharge from 100% SOC to 50% SOC with the battery delivering 47.85Ah at a 5.25A constant current load. The battery was then recharged for exactly 2 hours at .2C and then discharged back to 50% SOC and the stored energy for that cycle was measured.

The charge rate for this test was 21A and the timer set for 2 hours. If the battery could stay in bulk for two hours our maximum potential energy into the battery would be 42A. Because the battery hit absorption voltage, before hitting the 2 hour mark, we simply can not get 42Ah of energy into the battery…

CHARGING – 2 Hour Charge Test .2C – The Two Minute Mark

At two minutes into the test at 21A the battery terminal voltage is at 13.1V.

MYTH BUSTING: Think about this snap shot if you use or are considering a battery combining relay for charge management and are concerned or have been scared off by one of the many myths surrounding these effective and highly reliable devices.

The myth goes something like this: By using a battery combiner, on AGM batteries, and feeding the alternator or battery chargers charging current directly to the house battery bank first, “it will leave your start battery under charged“.

If you are practicing good battery management, and have even the minimum suggested charge current for an AGM battery, this is a complete non-issue. In 2 minutes of charging, at .2C or 20% of Ah capacity from 50% SOC, the AGM battery voltage is already at the “combine level” for the amazingly popular Blue Sea ACR.

Battery voltage will rise pretty slowly from here on but to get to an ACR’s “combine level” is relatively quick and easy, especially if you have your system set up properly. The Echo Charger, Duo Charger and numerous other DC to DC chargers also turn on at similar voltages and those devices require all charge sources to be fed to the house bank.

CHARGING – 2 Hour Charge Test .2C – Two Hour Mark

In this image the charge source is about to turn off when it hits the 2 hour mark. Net accepted current at 14.4V @ 1:58 is down to 11.6A.

DISCHARGING – 2 Hour Charge/Discharge Test .2C – Two Minute Mark

Here the electronic load has turned on and has now begun discharging the battery back down to 50% SOC. I did not pause and let the battery rest between charging & discharging because this is not actually done on cruising boats.

The object with this test is to see how much usable energy we can store in the battery in two hours at a .2C charge rate..

STORED ENERGY – 2 Hour .2C Charge/Discharge Test

After charging the battery from 50% SOC for two hours at 21A we were able to remove 35.28Ah’s and bring the battery back down to 50% SOC.

Let’s do the math: Baseline Ah Capacity = 95.69Ah

Discharge to 50% = 47.84Ah (left in the battery after discharge)

2 Hour charge then discharged and counted Ah’s delivered back to 50% SOC = 35.28Ah

47.84Ah + 35.28Ah = 83.12Ah of stored energy

83.12 is 86.9% of the baseline Ah capacity of 95.69Ah’s

RESULTS: The battery achieved approx 87% SOC from 50% SOC in two hours at a .2C charge rate

BEGIN: .4C – 2 Hour Recharge Then Discharge Test

Rather than bore you with multiple images that all look the same I am going to summarize the remaining three tests with the “stored energy” screen shot.

This test was a .4C charge for two hours and when discharged back to 50% SOC, after the 2 hour charge, the stored energy removed was 44.48Ah. While not a heck of a lot more than .2C it is the attained SOC that really makes .4C different.

Let’s do the math: Baseline Ah Capacity = 95.69Ah

Discharge to 50% = 47.64Ah (left in the battery after discharge)

2 Hour charge then discharged and counted Ah’s delivered back to 50% SOC = 44.48Ah

47.64Ah + 44.48Ah = 92.12Ah of stored energy

92.12 is approx 96% of the baseline Ah capacity of 95.69Ah’s

RESULTS: The battery achieved approx 96% SOC in two hours at a .4C charge rate

PERSPECTIVE: Charging to 100% SOC took 5:30 minutes so this means the last 4% of returned energy took 3.5 hours to complete at .4C and the first 46% of capacity could be returned in 2 hours at .4C. The problem still remains that the last 4% is critically important to AGM longevity.

BEGIN: .2C – 1 Hour Recharge Then Discharge

This test was a .2C charge for one hour and then discharged back to 50% SOC, after the 1 hour charge. The stored energy removed was 20.46Ah from a max charge rate of 21A.

CHARGE EFFICIENCY: As I have mentioned before bulk charging, where the charge source provides its full current before the battery reaches the limiting voltage, is nearly 100% efficient. Here we have a 1 hour recharge at a charge rate of 21A where the battery was able to store 20.46Ah of that 21Ah delivered to the battery. A 21A charge for 60 minutes is 21Ah’s of supplied energy. This means 97.4% of the energy supplied by the charger, or the 21A for exactly 1 hour, was removable as stored energy when we discharged back to 50% SOC. On this 1 hour .2C recharge the battery never attained the absorption voltage of 14.4V and was still in bulk when the charger turned off at the one hour mark. Bulk is very efficient!

SCALE IT UP: If we scale this test up, and it should scale well, a .2C charge rate on a 450Ah fairly typical cruising boats house bank would be a continuous 90A for 1 hour before your batteries even hit the absorption voltage set point. Yes, 90A continuously for 1 HOUR.. This is a metric $hit ton of work on a typical 90A – 120A alternator. This is why many a boater has burned up their alternators charging AGM batteries.

MYTH BUSTING: If you believe a battery monitor that counts Ah’s, and supplies a fixed charge efficiency number to the returned Ah’s (most all of them), can track your batteries accurately when you don’t recharge to 100% SOC with each cycle, this myth & lore is blown out of the water right here. In bulk this battery had returned energy efficiency of 97.4% yet the last 4% of returned energy, to 100% SOC, takes 3.5 hours! There is a major difference in charge efficiency throughout the SOC curve. Charge efficiency is not linear throughout the SOC curve, but most all battery monitors are linear in their application of charge efficiency. They simply apply a negative count factor for charge efficiency as the Ah’s are returned. For example if we return 10Ah’s with a 90% charge efficiency setting the battery monitor will only show that as 9Ah’s returned. If we were to stop charging in bulk we really do have closer to 10Ah’s returned. Do this a few times…….. Ouch! When you cycle more than a few times in the 50% to 90% SOC range there is no way for a typical Ah counter/battery monitor to accurately track your charge efficiency. For more info on this see the article on “Programming a Battery Monitor”.

Let’s do the math: Baseline Ah Capacity = 95.69Ah

Discharge to 50% = 47.44Ah (left in the battery after discharge)

1 Hour .2C charge then discharged and counted Ah’s delivered back to 50% SOC = 20.46Ah

47.44Ah + 20.46Ah = 67.90Ah of stored energy

67.90Ah is approx 71% of the baseline Ah capacity of 95.69Ah’s

RESULTS: The battery achieved approx 71% SOC in one hour at a .2C charge rate.

PERSPECTIVE: It is pretty clear that a 1 hour charge at .2C is an inadequate charge rate for AGM batteries that are routinely discharged to 50% SOC, unless you really like hearing your motor or generator run.

NOTE: Lifeline Battery recommends a .2C charge rate as the bare minimum for these expensive AGM batteries. Odyssey TPPL AGM batteries are recommended to be charged at a minimum of .4C.

BEGIN: .4C – 1 Hour Recharge Then Discharge

This test was a .4C charge for one hour and then discharged back to 50% SOC, after the 1 hour charge. The stored energy removed was 33.43Ah from a max charge rate of 42A.

SCALE IT UP: If we scale this test up, and it should scale well, a .4C charge rate on a 450Ah fairly typical cruising boats house bank would be a continuous 180A. This battery hit the absorption voltage point at approx 20 minutes when charged at .4C from 50% SOC. With a .4C charge rate your alternator or charger would only be in bulk, or running at its full output, for approx 20 minutes. While this certainly does not make the most efficient use of the alternator, or inverter/chargers, or generators it does charge the batteries to a higher SOC in a short 1 hour run.

Let’s do the math: Baseline Ah Capacity = 95.69Ah

Discharge to 50% = 47.98Ah (left in the battery after discharge)

1 Hour .4C charge then discharged and counted Ah’s delivered back to 50% SOC = 33.43Ah

47.98Ah + 33.43Ah = 81.41Ah of stored energy

81.41Ah is approx 85% of the baseline Ah capacity of 95.69Ah’s

RESULTS: The battery achieved approx 85% SOC in one hour at a .4C charge rate.

PERSPECTIVE: While .4C certainly does attain a higher level of SOC in 1 hour, approx 85%SOC, the gain in SOC makes pretty ineffective use of a .4C charge source while only utilizing it at 100% output for about 20 minutes. Most boaters charging AGM batteries would likely benefit from a compromise charge source current of about .25C to .35C for 1.5 – 2 hours +/- per day. Blended with solar you can get the bank to 85% SOC or so and let the solar take over for the long slow crawl back to 100% SOC.

The Difference Between .2C and .4C from 50% SOC to 100% SOC

Here is another way to look at the charge process with a doubling of charge current. In this diagram Bulk/CC is the orange area and Absorption/CV is represented by blue.

• At .4C the charge source is only working at full output, 42A, for 19 minutes then becomes voltage limited @ *14.4V
• At .2C the charge source is working at full output, 21A, for 1:16 before it becomes voltage limited @ *14.4V
• The difference in total charge time from 50% to 100% SOC, with this battery, when we doubled the charge current, was 12 minutes

NOTE: The blue charge acceptance curves are illustrative only. All times and voltages are accurate and taken directly from data points used in this test.

Another View of The Charging Process

Here is another way to look at the charge process. This was a *Lifeline GPL-31XT battery (125Ah rated that was charged at .15C or about 15% of its rated Ah capacity. *NOTE: This was not the battery being tested in this article, and it was used. This image is just for just for illustrative purposes..

BULK: If we start at the top left of the chart we can see that the current held rock steady at 18.75A for *1:42. This current, 18.75A is .15C or a 15% charging current of a 125Ah battery.

*NOTE: 1:42 of bulk charging (your alternator running at full bore) is more than enough to damage an alternator not otherwise protected for temperature or current limited to protect it. A charge rate of .15C would be an 80-90A alternator on a 400Ah bank, when accounting for the “hot” output, and not all that uncommon. I see lots of burned up alternators when they are under sized for the task.

VOLTAGE RISE: If we look at the left side of the chart we can see the voltage climbing to the absorption set point of 14.4V. It took 1:42 at 18.75A for the battery voltage to attain 14.4V.

1/3 From Left: This is the point where the charge current and voltage flip-flop. Voltage stops climbing and is held steady, and current changes from being steady/constant to declining. Once the BULK/constant current charge has driven the battery voltage to the absorption voltage limit, the voltage is now limited or held steady and the charging current begins to decline.

CHARGE TIME: As current declines, out towards the lower right of the chart, the time it takes to get that last few % in takes significant time. At .15C this slightly used AGM took a bit over 6 hours to reach 100% SOC. I have had sulfated AGM batteries take 7+ hours even at a higher .2C. The health of your AGM battery can impact your time to full.

TESTING SUMMARY:

50% to 100% SOC  @ .2C = 5:42 – Exited Bulk @ 1:16

50% to 100% SOC @ .4C = 5:30 – Exited Bulk @ 19 Minutes

50%  SOC @ .2C For 1 Hour = 71% SOC – Remained in Bulk

50%  SOC @ .4C For 1 Hour = 85% SOC – Exited Bulk @ 19 Minutes

50% SOC @ .2C For 2 Hours = 87% SOC – Exited Bulk @ 1:16

50%  SOC @ .4C For 2 Hours = 96% SOC – Exited Bulk @ 19 Minutes

DISCLAIMER: All batteries will test & perform differently based on age, type, chemistry and state of health. This battery and test are only really representative of this battery and test but should give some decent guidance as to what one may expect from a slightly used AGM battery. I purposely did not test a brand new AGM because that is not at all representative of what we as boaters have in use on-board our vessels for more than a short period of time. New batteries will perform differently but our batteries on boats rarely stay new for very long.

Good luck & happy boating!!

Battery After 20 Hour Capacity Test = 95.69 Ah Capacity

For this test I wanted to:

• Show the relationship of loaded voltage to SoC on a popular AGM lead acid battery.
• Utilize a battery not in perfect health to represent real world.
• Show why using a generic voltage to SoC chart may not work for your battery bank.
• Show the actual rebound voltage after discharging to 50% SoC under controlled conditions.

Customers SoC to Resting Voltage Chart

This image is an epic fail on our customers part, despite his very good intentions.

He located this voltage to SoC chart on the internet and I discovered it on his chart table. He was using it with resting voltages not under-load voltages as this chart was likely developed from. His battery bank was comprised of the identical battery being tested here.

If we cross reference this chart to the 20 hour discharge rate, under-load voltages, in this test they line up pretty closely but if using a chart like this for a RESTING VOLTAGE you will essentially be murdering your batteries.

Chart Resting Voltage              Actual Under-Load Voltage
90% 12.75V                                                      12.55V
80% 12.50V                                                      12.50V
70% 12.30V                                                      12.37V
60% 12.15V                                                       12.24V
50% 12.05V                                                      12.11V

Please be aware that some charts on the internet are for resting voltages. A resting voltage is 12 – 24+ hours of no loads or charging at 77°F. The “at 77°F” is absolutely critical because at temps above 77°F surface charge dissipates more rapidly and at temps below 77°F the surface charge dissipates more slowly.

As I type this I have a fully charged AGM battery in my storage barn that has been sitting 100% disconnected for well over a month, and the resting voltage is still 13.12V. Why? The battery temp is close to 40°F  right now and has not been much above 45°F since I set the battery in storage. I know this battery will rest at 12.93V once the surface charge has dissipated, but at 40-45°F this can take weeks or as long as a month or more.

Voltage to SoC Charts:

A Voltage to SoC chart should only come directly from the manufacturer of your batteries, or through physical testing of your own batteries, as I have done here. You should avoid the use of use generic charts off the internet. Why? Because every battery manufacturer will have a slightly different voltage performance curve under load. Deep Cycle AGM will be slightly different than dual purpose AGM or TPPL AGM or GEL or flooded etc..

Some charts you find on the internet do represent a “resting voltage” , but you’ll also find some for a 20 hour discharge rate or an under-load voltage. If you’re using voltage as an indicator of SoC, the rate of discharge, as well as battery temperature, can also affect your SoC to voltage points. Cyclic On/Off loads, like we have on a boat, can also tweak this relationship. Using the wrong Voltage to SoC chart only exacerbates issues related to using voltage for SoC estimation. Using the wrong chart can actually accelerate the murdering of your batteries.

Voltmeters:

On top of using an incorrect Voltage to SoC chart, using an inaccurate voltmeter or one connected or voltage sensed in the wrong location can also impact you negatively. Always use a good quality, known accurate voltmeter that can display out to the hundredths position, not just the tenths position. For example, a voltmeter that only reads 12.1 volts gives too little information. A voltmeter that can read 12.15V, or adds the hundredths of a volt position, will give you far better trend information. The voltmeter should have both it’s negative lead and positive lead directly sensing/measuring the house banks physical battery terminals, or within a few inches of the bank on a distribution bus fed by large gauge wire. Sensing voltage anywhere else in the system can lead to erroneous voltage readings due to circuit voltage drops.

95% SoC – 5.25A Load – Volts =12.59V

The battery used in this test is a very popular AGM, a Lifeline GPL-31T.

It is factory rated at 105Ah, at the 20 hour discharge rate, but this particular battery, off my brothers boat, was used and only capable of delivering 95.69 Ah’s. I chose this slightly used battery to represent a more “real world” scenario. A 20 hour discharge rate is simply:

Ah Capacity ÷ 20 = X

For this 105Ah rated battery the 20 hour discharge rate looks like this:

105Ah ÷ 20 = 5.25A

Despite the slightly diminished capacity, 91.3% of the factory rating, I chose to keep the discharge rate at 5.25A at a controlled battery temp of about 76.4°F. Ideally I would have liked to have spent the time to figure out the new 20 hour discharge rate but this entails numerous tests to 10.5V and was not critically necessary for this experiment, as no boat owner will ever do this.

The 5.25A discharge rate is slightly higher than what this battery can actually deliver for 20 hours, but close enough to make the points I wanted to share here. Perhaps less than .02% of boat owners ever test their batteries for actual Ah capacity, so using the 20 hour rate on this battery is still quite realistic.

For a 20 hour test, or to see where your bank stands against how it is rated for Ah capacity, a 20 hour SoH (state of health) discharge test is performed. To perform a 20 hour test the battery is first charged to 100% SoC and then it’s allowed to rest for 24 hours. It is then discharged at a constant 0.05C discharge rate or Ah ÷ 20= X to a terminal voltage of *10.5V. The Ah’s or time at discharge rate is then calculated to show the percentage of the rated Ah capacity the battery could deliver at its current SoH. A discharge rate of 0.05C is equal to 5% of the batteries 20 hour rated capacity so 5% of 105Ah is 5.25A.

*Assumes a 12V battery. During a 20 hour Ah capacity test the battery is discharged to 1.75V per cell.

On a cruising boat the battery bank would be considerably larger and a 20 hour discharge rate, at bank level, would look like this:

• 200 Ah Bank = 10A Discharge Rate @ 77°F
• 300 Ah Bank = 15A Discharge Rate @ 77°F
• 400 Ah Bank = 20A Discharge Rate @ 77°F
• 500 Ah Bank = 25A Discharge Rate @ 77°F
• 600 Ah Bank = 30A Discharge Rate @ 77°F

90% SoC – 5.25A Load – Volts =12.55V

In this image the battery is at about 90% SoC with an under-load voltage of 12.55V.

On a 400Ah bank this would be a 20A load in order to see this voltage at 90% SoC.  If you were discharging at 8A and saw 12.55V you would be at a lower SoC than 90%.

85% SoC – 5.25A Load – Volts =12.52V

Here we are crossing the 85% SoC mark at 12.52V. As cruising boaters the average discharge rate is almost always far lower than the 20 hour rate, and should be lower.

A typical cruising boat with a 400Ah bank will be discharging, on average, somewhere in the 5-6A range if averaged over a 24 hour period. Your under-load voltages should not drop this fast with healthy batteries. Conversely your SoC to loaded voltage will also not be the same as here. At the voltages to SOC show here, your SoC will actually be lower when discharging at a lower discharge rate. The reason for this is due to the Peukert Effect or what some call Peukert’s Law.

80% SoC – 5.25A Load – Volts =12.47V

Here the battery at about 80% SoC under the same continuous 5.25A load, and we are at 12.47V.

Voltage can be used as a guide for SoC but you really need to know the voltage performance of your battery bank, against a known discharge rate, and it takes work to figure this out. Of course once you’ve figured it out,  the voltage behavior under-load will change on you as the batteries age.

There is also another gotcha in the mix that I should mention. Loads that cycle on and off give the battery rest periods which also change and modify voltage performance at XX load. If your loads cycle on and off, and you choose to use voltage for SoC, you may be over-discharging your bank and never even know it.

This is why a generic *OCV to SoC chart will rarely help the average boater, and often serve to actually help prematurely damage the batteries.

*OCV = Open Circuit Voltage Reading

75% SoC – 5.25A Load – Volts =12.42V

Over the years I have realized that most boat owners drastically over discharge their battery banks when using voltage as a predictor.

In a recent battery use survey on SailboatOwners.com there were over 1000 responses, of which 98.4% were from sailboat owners. The survey was about marine battery use. Of those 1000+ responses, 1188 to be exact, 72.42% of respondents regularly discharged the bank below 12.1V. As Homer would say…. D’oh!!!!!

What’s bottom line with lead acid batteries?

Even at your average house loads the terminal voltage should not be dipping below 12.1V, when discharging at the 20 hour discharge rate.. That is if you expect any sort of decent cycle life from them. As you will see in this experiment, under a 5% load to Ah capacity discharge, 49.3% SoC is achieved, under load, at 12.10V. Most boaters however don’t discharge at the 20 hour rate, so read on.

70% SoC – 5.25A Load – Volts =12.37V

Here we are at 70% SoC and 12.37V.

Compare this to the chart from above at 12.30V that our customer was using as a resting voltage chart. This is not a resting voltage, it is an under-load voltage, and the battery has been under a constant 5.25A load now for nearly five and a half hours straight. If you were expecting a 12.30v resting voltage to represent 70% SoC, you are now way below 70% SoC…. Oops…..

65% SoC – 5.25A Load – Volts =12.30V

65% SoC under-load voltage = 12.30V.

60% SoC – 5.25A Load – Volts =12.24V

60% SoC under-load voltage = 12.24V…

55% SoC – 5.25A Load – Volts =12.18V

55% SoC under-load voltage = 12.18V…

50% SoC – 5.25A Load – Volts =12.11V

Here we are at 50% SoC, based on the -Ah removed from a baseline, under a capacity test.

It took approximately 9 hours at a 5.25A load to get to 50% SoC and the under -load voltage is still 12.11V. To put this in perspective, when this battery was discharged at 2X – 2.5X your average cruising boat house loads, the bank is crossing the 50% SoC threshold at approx 12.1V. This means on your average bank you had better be discontinuing any discharging at somewhere around 12.15V to 12.2V+.

If you expect or plan to use voltage as your indicator of SoC, and as an indicator of when to re-charge, I would strongly urge you to begin recharging at a maximum under-load voltage of 12.1V. You will be far better served to begin recharging at 12.2V or greater because your average discharge rate will be lower and you will also have cyclic loading of the battery which can artificially inflate a Voltage to SoC reading.

If your average house loads are a lower average load than the 20 hour discharge rate,  you will be better served to begin re-charging at a low of 12.15V – 12.2V+, in order to get the best cycle life from your bank.

49.3% SoC – 5.25A Load – Volts =12.10V

Here’s why I suggest you begin recharging at 12.15 -12.2V because at 12.1V this battery is already at 49.3% SoC while being discharged at 5.25A at 76F.

Resting Voltage – Approx 16 Hours @ 49.3% SoC @76°F = 12.32V

In this image the battery is at 49.3% SoC based on removed ampere hours.

The resting open circuit voltage has rebounded to 12.32V. If you had been using our customers chart for resting OCV you would have mistaken 49% SoC for 70% SoC and kept on DISCHARGING the bank. Ouch!

With this test it’s easy to see how battery assassins commit battery murder without even being aware of it. Please understand and use voltage for SoC very carefully. Also, keep in mind that as your batteries age they will cross a voltage threshold differently than they did when new. The only way to know this performance is to physically test for it.

For most boat owners we strongly recommend using a self learning battery monitor, for SoC, such as the  Balmar SG200

Points to Ponder:

• Always get your Voltage to SoC data directly from the physical manufacturer of your batteries, not from the net.
• Make sure you know what your voltage to SoC chart represents; eg: “resting  voltage” or  “under-load voltage”. They both exist and are not the same.
• Study and learn your batteries voltage behavior, under your average on-board loads. Run experiments if you need to.
• Use a known accurate voltmeter that displays to the hundredths position.
• Your voltmeter should only sense voltage at the battery bank terminals.
• Discharge rate affects your Voltage to SoC relationship.
• Cycling discharging affects your Voltage to SoC relationship.
• Battery temperature affects your Voltage to SoC relationship.
• Aged batteries affect your Voltage to SoC relationship
• As your batteries age the voltage behavior will also change.
• Battery temperature directly impacts the time it takes to attain an accurate resting voltage.
• Keep it simple, don’t discharge your Lifeline AGM bank below 12.15V to 12.20V even under your average house loads.
• Recharge your batteries to 100% SoC as soon as possible after each discharge.

Good luck & happy boating!

Note The Melting of The Battery Case

(originally published July 2012)

The connections to your batteries matter. How you make them, how you torque them and how clean they are all matter. Not following best practices or marine wiring standards can impact your personal safety.

While doing a winterization, and getting ready to equalize these batteries, I noticed something strange that I could not really put my finger on, then it hit me.

The battery case around the positive post was melted and uneven looking. When I grabbed the positive battery cable it was physically able to twist on the post with just minimal pressure.

Upon closer inspection it was apparent that the battery terminal had gotten so hot that it began melting the plastic of the battery case.

Why? Read on…..

The Nyloc Nut Still Had Plenty of Resistance & “loc”

I am not one of those marine insiders who is in the camp of “Nylocs are bad on battery terminals“. This example showed that the failure mode was not in-fact the Nyloc nut. I could not back this nut off with my fingers, even after it was loosened with a wrench. The plastic battery case melted well before the Nyloc failed to “loc” / lock.

Battery cases are made of polypropylene and Nyloc nuts are made of nylon, which has a higher melting point than the battery case does.

I do prefer to see a locking washer on battery post studs but sometimes they simply don’t fit, where a Nyloc may. In either case the nut must be properly torqued to battery manufacturer specifications, this nut was not.

The nut coming loose or vibrating loose was not the problem or the root issue here. This problem was simply poor installation practices.

The issues were:

#1 The Nyloc nut was not correctly torqued and showed clear evidence of pliers or another unsuitable tool being used for tightening.

#2 The lug had a SS flat washer placed under it. A SS flat washer should never be inserted between the lug and battery terminal. It is perfectly okay to use it under the nut, but it must remain on top of the lug & never underneath the lug.

The ABYC Standard that covers this:

Below: The correct installation sequence for a battery lug. A washer never goes between the lug and battery .

Why no Stainless washers between the lug & battery?

Below is a chart showing the conducting properties of varying metals. As can be seen, stainless steel is a very poor conductor.. A stainless washer creates high resistance, which leads to heat..

Holy meltdown Batman

This image represents the inherent failure potential when we connect our battery banks to high current devices such as large inverters, alternators or large inverter /chargers and we slap a washer in between the battery and the lug.

Image courtesy Heritage Marine Electrical

Nyloc Nut Deep-Dive….

I hear and see it stated quite frequently on the interweb not to use Nyloc nuts on batteries. The supporters then trumpet this around thenet as fact without doing any sort of critical thinking. Unfortunately they line up to defend this sentiment without doing any sort of research or examination of actual facts. Okay fine, it’s the interne. Let’s examine this a bit..

Safe Working Range vs. Melting Point

The Nyloc nutswe  use at Compass Marine Inc. are rated to 140C for the safe working range or “operating temperature range”. This is 284F.. If your batteries get to anywhere close to 284F you have other major issues to deal with! To put this into perspective, even the best marine UL 1426 battery cable is rated to just 105C or 221F. Sadly there are still thousands and thousands of boats out on the water, built in the 70’s & 80’s, using 60C / 140F rated battery cable, sad but true. If the Nyloc in the nut will melt and cause a failure then I suppose we may all need at least 140C rated marine wire too?

Of course we can’t just look at the safe working range if we want to see the point where an actual total failure might occur. Where would that likely occur? Probably somewhere well above the 284F safe working temp and closer to the melting point for the nylon 66, which is used in Nyloc nuts.

The actual melting point of the nylon 66, used in Nyloc nuts, is 515.9F. For examination purposes however, we can still use the safe working temp of 140C/284F.  What if you have soldered battery lugs? If you do, it is quite probable that you have a solder that actually melts at a lower temp than Nylon 66 does.. Yes, you read that correctly. Many electrical grade solders melt at a lower temp than the nylon used in a Nyloc nut does.

The point here is that the ABYC standards still allow soldered on battery lugs (with no mechanical connection eg: crimp) and the solders above are very typical of electrical work such as soldered on battery lugs..

Battery Case Melting Point?

What about the plastic used in the actual battery cases? Lead acid battery cases are made of polypropylene (PP), not nylon. Polypropylene (the battery case) actually melts at around 189F lower than the nylon 66 in the Nyloc nut does. We are seeing exactly that right here in this case. The Nyloc nut survived with plenty of locking still intact, yet the battery case had begun to physically melt.

I suppose we’d best get rid of those unsafe plastic battery cases and replace them with STEEL… Oh wait steel & acid, hmm better think this one through a bit more……..?. (grin)

What fasteners do battery makers ship batteries with?

Let’s also look at the way the vast majority of batteries for marine use actually ship to us? An insanely large percentage of “marine batteries”, even today, and our business installs hundreds of batteries still ship with hex nuts but, no locking washer. Yes, you guessed it, there is no lock washer to be found with many of the marine battery brands. Heck, there are still some brands shipping with wing nuts and no locking mechanism what so ever. The ABYC actually disallows wing nus for batteries using 6 AWG or larger wire.

Exide Marine Battery:

East Penn / Deka Marine Battery:

Exide and East Penn/Deka/Duracell (East Penn licenses the Duracell name) own a huge percentage of the marine market yet neither bothers to ship any locking mechanism. How is it that replacing a standard hex nut (no washer) with a Nylock is “worse” or “less safe”, than what these manufacturers ship batteries with? The answer is clear, a Nyloc nut would be safer than just a hex nut. I agree that these SS hex nuts are far superior to “wing nuts” but cutting corners on a locking mechanism is just poor form. I have many other images of “marine batteries” that do not ship with locking washers but, I won’t boor you. The way most batteries ship, without any locking washers, your failure mode is just one failure point, improper torque. Add a Nyloc and you now need two failures before anything bad could happen. Add a locking washer on top of a Nyloc and now you’d need three failures.

There are however a good number of premium battery battery makers, who actually do supply locking washers, such as;

• Odyssey
• Northstar
• Firefly
• Victron
• Full River
• Rolls
• Lifeline
• Mastervolt
• Lithionics

Plus just about every LiFePo4 prismatic cell manufacture I know of. All the batteries brands I just mentioned can deliver MASSIVE amounts of short circuit current into a dead short.

How many installers or folks that DIY do you suppose add any locking washer or Nyloc nut beyond what the battery manufacturer supplied the battery with? From our observations, as a marine electrical business, I can say that this number is about as close to 1% as it gets. A nut only may be okay, if the nuts are properly torqued, (each manufacturer provides a torque spec), the cable is properly strain relieved, and the battery physically can’t move, but I rarely see that. The ABYC standards actually allow for batteries to move slightly, up to 1″, and this is why some level of locking is considered a best practice.

A Simple and Honest Question:

Would using a Nyloc nut be worse than what many battery manufacturers shipped the battery with, if it’s a plain hex nut or wing nut?

Answer = NO! Adding a Nyloc is a level of safety beyond a standard hex nut or wing nut.

In this melted battery case, the Nyloc nut was still well “locked“, despite the battery case physically melting due to high resistance. I’d have to vote for the Nyloc certainly being better than no locking mechanism at all.

Why does all this matter?

Before your Nyloc nut can melt, the battery will have likely already begun to melt, as it did here. Even if you somehow exceeded the 284F, and and your battery has not exploded, and the Nyloc nut failed to perform its locking feature, this can only be considered a secondary failure when compared to what most batteries ship with. Before we can even get to a Nyloc failure, we would still need to have a primary failure or a nut torque failure first.

In this case we had a primary failure mode, lack of proper nut torque, which lead to high resistance and then to the battery case melting and the heat shrink melting. A physically melted battery case, and the heat shrink melted and yet a secondary failure of the Nyloc nut still did not occur.

We would need two failure modes to have the actual failure of a Nyloc nut. A melted Nyloc and an improperly torqued nut to begin with. Based on the factual data, including melting points, this suggests that before this Nyloc nut would have failed the battery case would have been so melted the owner would have been alerted to something, such as a fire or acid all over his vessel, well before the Nyloc nut became an issue.

Items That Melt Before the Nyloc:

– The battery Case
– Heat Shrink
– Solder
– Wire Jacket

But the Nyloc is the one that gets the bad rap by “docksperts”(dock experts)on the net??

In our business we see thousands of battery posts every year with no locking mechanism. Do we carry lots of 5/16″ and 3/8″ lock washers and 5/16″ and 3/8″ nuts,  & wire ties, you bet we do. We also however carry a lot of 5/16″ and 3/8″ Nylocs too and in cases of short battery posts, such as Trojan batteries. We also carry flanged self-locking nuts also called Wizz nuts. We go through multiple boxes of 100 each of lock washers and Nyloc 5/16″ and 3/8” nuts every year.
My personal preference here is to use a locking washer when ever I can, but when it won’t fit, I have no issues using a properly torqued Nyloc nut on a battery terminal.

Why Do Battery Manufacturers use Stainless Nuts and Posts if Stainless Steel is a Poor Conductor?

The answer to this is simple. The connection to the battery is between the lug and lead not the SS fasteners or SS posts. The nuts and posts are only there to provide compression and resist corrosion. Stainless is a fine solution to accomplish this.

How often do I see regular hex nuts, like price-point sensitive battery manufactures ship the product with, that lack a locking washer, actually come loose? Not all that often but, I do see it.. When I do, there are often signs or evidence they were tightened by a pair of pliers, as was  the case here.

When tightened with a wrench, & properly torqued, it’s actually pretty rare to see a loose standard nut, even without a locking washer, come loose. When I do see this the battery installation has been sloppy, allowed too much battery movement and had sub-optimal strain relief for the large gauge wire. The key words are “properly torqued“. Properly torqued is the reason the ABYC, USCG  & marine industry has moved away from allowing wing-nuts.

Boat owners and sloppy marine techs far to often opt to not to use a wing nut wrench or pliers to apply the proper torque. They improperly believe proper torque means with thumb and fore finger. It’s simply not possible to properly torque a wing nut with your thumb and fingers. It is also not advisable to torque standard nuts with a pair of cheap pliers. Would you torque your vehicles lug nuts with pliers………..??

I can personally point to numerous instances of loose wing nuts, but not a single case where a Nyloc came free because it melted and then vibrated loose. In almost every case of a wing nut coming loose it was because the installer made the nuts “finger tight” which is a far cry from properly torqued..

It’s also interesting to note that the ABYC safety standards specifically prohibit wing nuts above 6GA wire but they make no such prohibition for Nyloc nuts.

My only point here is to suggest that I would prefer to see a Nyloc used rather than the option of a regular nut with no lock washer or a wing nut with no lock washer. My first preference, if it will fit the post, is for a Nyloc nut and locking washer, second choice would be a hex nut with lock washer, as many premium battery makers ship with. A Wizz nut would be a third choice. The fourth choice a regular nut without a locking washer. All of these choices, of course, properly torqued.

Unfortunately, there are situations where a regular nut height, or even a half-height nut is all that will fit on the post & Trojan Battery is notorious for supplying extremely short posts. In this case proper torque and the use of a Wizz/Serrated Flange Nut nut is a must. A standard Wizz nut is the same height as a standard nut but has a built in serrated locking washer.

CAUTION: Using Wizz nuts for batteries that will be decommissioned each winter can reduce the thickness of the lug over time. The reversing of a properly torqued Wizz nut causes copper and tin plating on the terminal to be removed more so than that of a standard locking washer/flat washer combo or a Nyloc/flat washer combo. You can out a flat washer under a Wizz nut but the entire point of a Wizz nut being used is due to a lack of battery terminal height.

Rant officially over…. (smile)

It Actually Got Hot Enough To Melt The Heat Shrink

This lug got very, very hot, hot enough to physically melt adhesive lined heat shrink. Even my industrial grade Milwaukee heat gun has never melted heat shrink like this.

It should also be noted that this battery was protected by a 200A ANL fuse. The fuse and holder are perfectly fine and never blew. Why? Fuses won’t and can’t protect against high-resistance which is what caused this situation. A high-resistance situation can start a boat fire at well below a fuses trip rating.

Huston, We Have a Problem…!

Here’s the other half of this problem. The first half was caused by improper torquing of the Nyloc nut with pair of pliers. Please DO NOT use pliers to tighten and torque battery terminals.

The second problem arose because the person who connected these batteries left the flat SS washer on top of the lead battery post. This means the SS wahser was sandwiched between the lug and the lead of the battery post. Stainless steel is a horrible conductor, one of the worst.

In battery installations flat washers should never be placed between the lug and battery post. They can only ever reside on top of the lug compressing it not being compressed.

Here’s the relevant ABYC standards from E-10 Storage Batteries:

“10.8.3 Battery cables and other conductors size 6 AWG (13.3 mm²) and larger shall not be connected to the battery with wing nuts.

10.8.4 Multiple conductors connected to a battery shall be installed with the highest ampacity conductor terminal closest to the battery, followed by successively smaller ampacity conductor terminals.

10.8.4.1 A maximum of four conductor terminals shall be permitted to be installed on a single battery stud.

10.8.5 Flat washers, if used, shall only be installed immediately under the split lock washer and nut of the attachment stud.”

The Case & Post

Here’s another shot, and close up, of the melting of the plastic case around the positive post. This battery will now be retired because its ability to hold electrolyte may have been compromised. We have no way to see inside, to inspect actual damage to the electrolyte post seal, so as a safety precaution this battery will be recycled, even though it still tests fine. Sad really.

If you click on the photo, and look closely, this terminal does not appear to have been cleaned before the terminals were re-connected in the spring. There are signs of “hot spots” in the lead and what appears to be some melting close to the stud too.

This termination point was creating tremendous resistance and lots of heat thanks to a combination of not just one, or two terminal installation errors but a third as well. The third failure mode here is that poor cleaning and housekeeping of the terminals themselves was evident.

Another View

Here’s another view of the physical melting, of the battery case, around the base of the post. It should not look like this. Issues like this can start small but can quickly  become quite problematic, especially if left unchecked.

Please keep a watchful eye when connecting and disconnecting your battery banks for anything unusual.

I apologize for the poor quality photos. The lighting on this boat was rather pretty poor.

Lock Washers

This particular battery is an extremely high current capable AGM variant called TPPL or thin plate pure lead. This Odyssey, a single group 31, can deliver 5000A of current into a dead short. You really don’t want your connections loose on a battery like this. EnerSys, the parent company of Odyssey, thinks it’s important enough to include a “locking mechanism” or lock washer with their product as do many other premium battery manufactures. In this image the kit is still taped to the battery as it shipped.

Trojan Battery Document

This image is from a document I received at a Trojan Battery training seminar at a solar conference. In this document Trojan is saying exactly what myself and the ABYC standards say. You can not place a washer between the lead or brass battery terminal and the cable lug because it creates a high resistance point which can lead to a melt down.

Also note where Trojan Battery is showing the use of lock washers despite only currently including washers with their Reliant AGM batteries. Perhaps the lack of a locking washer, on some of their flooded products, is due to the “shrinking post syndrome” some of their batteries have been suffering from that feature the ELPT (embeded low profile post) terminals.

In this image and illustration we can actually see where the ABYC weighs in as highlighted in yellow.

Light Cycle vs. Deeper Cycle

NOTE: This article deals with FLOODED marine batteries, not AGM or GEL batteries.

The Problem:

The problem, as I see it, is one of dishonest marketing where multiple battery types wear the same clothes (sticker) and will perform differently when placed into a deep cycling situation. Sadly, the standards board in the USA, Battery Council International (BCI), allows for this foolishness.

Does this mean a Group 24, 27 or 31 battery can’t and won’t work? Absolutely not, it just means that when compared to a battery that is actually designed, built and intended for deep cycling activity, such as golf car, sweeper scrubber or fork truck batteries a Group 24, 27 or 31 flooded battery simply is not the same, cycle-wise, despite the “sticker” suggesting to a buyer that it is.

Unfortunately the industry has no real marketing definition of what “deep cycle” means so any battery a manufacturer feels they want to slap a “deep cycle” sticker on, gets one. This range of  deep cycle labeled batteries spans all the way from a Group 24 12V automotive cased battery up to and including massive 15-20 year expected life 2V cells used in stationary applications. A 2V cell is obviously more “deep cycle” than even golf car, fork truck or sweeper scrubber batteries but all may wear the same deep cycle sticker. If you buy batteries more carefully, you can get more life out of them, for your dollar.

As a marine electrician I get to see, replace and test lots and lots of batteries. Because of this I also need to know quite a bit about batteries, how they work, how they charge, how they cycle, which ones are best suited for the application and above all else, how they are marketed. Suffice it to say, this last point, the marketing, is my biggest bone of contention.

I also test batteries for their actual Ah capacity ratings on a near daily basis. As I type this I have two 20 hour tests in-process. When I began doing actual 20 hour testing, about 17-18 years ago, my set up was crude but it worked OK. I quickly began to see a sharp differentiation between how 12V Group 24, 27, 31, 4D & 8D batteries were holding up when compared to industrial use deep cycle batteries such as golf cart, L16’s J305’s etc.. As time moved on I invested more money into better capacity testing & charging equipment to get much more repeatable and more accurate capacity data. My test stations even include temp controlled water-baths so battery temp is not a factor.

On occasion I hit a point where I become so frustrated with bovine-dung marketing that I must simply explain myself. What I believe should be obvious, is not always so obvious, especially when the marketing departments muddy the waters. This article is one of those cases where I have simply had enough of the bovine-dung and have to get this out there so boaters will have a better understanding of what they are really getting, or not getting, when they plunk down a pile of greenbacks for a set of “deep-cycle” batteries. Let this rant begin…….(wink)

First let me summarize this article in a sentence or so. This is so you can bypass the wordy diatribe if you must..

Group 24, 27 & 31 & most *4D & *8D flooded 12V “Marine Batteries” are NOT really a deep-cycle battery when compared to a battery specifically designed from the ground up as a “deep cycle” battery. Simple stuff.

*There are only two companies I know of producing 4D or 8D deep cycle flooded batteries, comparable to Golf Car batteries in terms of cycling, and they are Dyno and Rolls.

There are 2V, 6V and 12V flooded batteries that are better suited to cycling duty than the typical Group 24, 27, 31 , 4D or 8D automotive cased batteries. If you have the height to fit 6V or 12V golf car, sweeper scrubber or industrial batteries you certainly can get a lot more for your money.

Battery Buying Misinformation: “You purchase deep-cycle batteries based on Ah & cost“

Battery Buying Reality: You purchase deep-cycle batteries based on Ah, cost and cycle-life

If you’re failing to include “cycle-life” in the battery buying calculation you are only robbing yourself..

Let’s go through how far too many boat owners buy batteries;

#1 Boat owner walks into West Marine or battery dealer and says “I need a new battery for my boat.” Dealer or West Marine associate says “What size?” and the owner says “They look like that.” The associate then asks whether the boat owner will be starting the motor only or starting the motor and using electronics with it? Owner answers yes about starting and electronics and walks out with a 12V group 24, 27 or 31 “Marine Dual Purpose” battery for a deep-cycling application…. This transaction = FAIL

#2 Boat owner walks into West Marine or battery dealer and says “I want a house bank battery with the most capacity.” Associate looks at the reserve capacity (RC) or Reserve Minutes (RM) rating and tells the buyer; “Here’s a Group 24 130Ah battery.“. The boat owner leaves thinking he just bought a massive 130Ah Group 24 12V battery. Sadly, no such battery exists on this planet. D’oh… This transaction = FAIL

There are plenty more scenarios I could play out here but the main point is that the average boat owner often has little understanding of how to buy & choose a battery properly suited for deep-cycling use.

Deep cycle use, for most battery manufacturers, is considered drawing the battery to 50% state of charge, on a fairly regular basis. The boat owner however is not alone in their lack of education because, even the associates at many battery retailers don’t have a clue about the products they are selling.

It is not my intent to pick on West Marine in this article but seeing as they have the published data in their catalog, which most battery buyers entirely miss or gloss-over on, I thought I would walk through the battery buying process for the average flooded battery buyer so that you, as a battery owner, are armed with information to purchase the right batteries for your vessel.

Key Points:

Ampere Hours (Ah’s) and Reserve Capacity / Reserve Minutes (RC) are not one in the same nor are they interchangeable. You want to purchase house bank cycling batteries based on the Ampere Hour rating at the 20 hour rate not the Reserve Capacity or Reserve Minutes rating. If the battery does not have a 20 hour Ampere Hour rating it is generally best to simply walk away, or find out who actually made the battery.

When I say “who made the battery” I am talking about the physical manufacturer, not the re-seller who simply slapped a sticker on it. You then call the manufacturer and find out the 20 hour Ah capacity rating for that battery, if it even has one. Some batteries are tested for a 20 hour rating but the sticker brands often leave this data off.

Worse yet is that some Group 24, 27 31 etc. batteries have their 20 hour rating “calculated” from a reserve minute or reserve capacity testing. What? All this means is the battery you may be buying was never physically tested for an actual Ah rating and they used a mathematical calculation to try and predict the 20 hour rate. An RC test is is usually conducted at 25A and an Ah capacity test is one which allows the battery to run for 20 hours at the 20 hour discharge rate. For a 100Ah battery this would be 5A. That same battery when tested for reserve capacity would be discharged at a 25A rate. The mathematical translations from RC to Ah capacity do not always work out accurately. Many Group 24, 27, 31 etc. batteries, that I have tested, have a very, very tough time delivering their actual Ah capacity rating even when new and cycled for break in.

Misleading Marketing:

Not all marketed “Deep Cycle” batteries are in fact Deep Cycle batteries. The vast majority of 12V flooded batteries sold as “Marine Deep Cycle” are not really what should be considered a deep cycle battery. I often refer to 12V flooded deep cycle batteries as light cycling or pseudo deep cycle batteries. While there are a few exceptions to this rule, such as 12V golf cart batteries and 12V sweeper/scrubber batteries, you won’t find them most marine retailers such as a West Marine.

As mentioned above Group 24, 27, 29, 30, 31, & most 4D & 8D flooded batteries are simply not a deep cycle product when compared to a battery such as a golf car battery, sweeper/scrubber battery or any other industrial application deep cycle batteries. GC2 6V batteries usually cost less than 12V batteries on a per ampere hour basis and also usually yield double the lab cycle life rating or more..

The term “Deep Cycle” has been badly bastardized by the industry to the point that it is almost entirely meaningless. You as the buyer should educate yourself as to what really represents a good value before buying batteries..

Deep Cycle Battery Questions to ask Yourself:

1. What is the 20 hour Ah rating?
2. What is the “lab rated” cycle life of the battery when compared to other batteries within its own brand?
3. What is the Cost per Ah?
4. What is the cost per lab-cycle?
5. What is the largest Ah capacity battery I can fit?
6. Can the manufacturer provide you a Peukerts constant so a battery monitor can be programmed?
7. Is this a good quality battery made by a reputable manufacturer?
8. Who actually manufactured this battery? (Not who put the sticker on it?)
9. What is the warranty? (do not get hung up on this)

What is the most important part of this equation, that is almost always left out? If you guessed step #2, you win!!!!

Lets use the points just made to purchase the pictured batteries:

Group 24 “Deep Cycle” 12V:

• Group 24 Deep Cycle = 75 Ampere Hours or 150Ah’s for two. (you’d need two of them for any usable house bank)
• Group 24 Deep Cycle = 350 lab rated cycles to 50% DOD
• Cost per Ah = $2.07 For a 150Ah bank
• Cost Per Lab Deep Cycle = 97¢ *per cycle – *expect half the rated cycles/real world = $1.94/Cycle

Group GC2 6V “Deep Cycle” (requires two for a 12V bank):

• Group GC2 6V = 230 Ampere Hours (two 6V batteries in series = 12V bank)
• Group GC2 Deep Cycle = 850 (took mid range) “lab rated” cycles to 50% of capacity
• Cost per Ah = $1.74 For a 230Ah bank
• Cost Per lab deep cycle = 47¢ *per cycle – *expect half the rated cycles/real world = 97¢ per lab Cycle

In virtually the same foot print as two Group 24 12V light cycle batteries, only slightly taller, two 6V batteries wired in series for 12V will yield approximately 850 lab cycles vs. 350. It will also yield 80 more amp hours of capacity in virtually the same exact foot print. The cost per Ah, based on West Marine prices, is considerably less and the cost per lab cycle is approx half. This is exactly why the battery buying calculation must always include cycle life not just Ah to $$.

My point here? Don’t forget to look into the lab rated cycle life and then purchase batteries that can theoretically deliver you the most cycles. We must remember that lab cycles are a theoretical best case for “real world” use. This cycle life data can be used as guidance within a brand. In other words lets stop focusing on what the “sticker” says, hell they all say “deep cycle”, and focus on the expected durability of the battery in a cycling application.

Fitment of Batteries:

Unless the builder has left you no additional height at all, in the battery compartment, a GC2 6V or GC-12 golf car battery can very often fit where Group 24, 27 or 31 batteries did. A GC2 (T-105) golf car battery will fit into virtually the same foot print as a Group 24 battery only it will be slightly taller..

Dual Purpose vs. Deep Cycle

Pictured here is the lab rated difference between a golf cart battery and a Dual Purpose Group 24, 27 or 31.

The West Marine Advisor – Cycle Life

Just in case you wanted to see where you can actually reference the *data points am discussing, in regards to the West Marine Sea Volt/ East Penn product, you can find it in the West Marine catalog. This chart is on page 379 of the 2014 West Marine catalog..

When buying batteries for deep cycling use, always be sure you can get your hands on manufacturer cycle life data to compare their batteries across types. No data? No buy…….

*Data Points: I have confirmed this data to be accurate, with West Marine, to the best of their knowledge. The data in this image comes straight from West Marines supplier, East Penn Manufacturing which is also known as Deka.

East Penn Golf & L16 Chart

So what’s the bottom line between golf cart batteries (GC2), L16’s, J305’s, GC-12/T1275/J-150/9C12/921’s and light-cycling 12V Group 24, 27, 31 etc.? Below is the answer one of the largest US battery makers gave to us when we asked this very pointed *question. (*Source email string between Marine How To and battery manufacturer testing engineer.)

Question asked by Marine How To.com:

Q: “If the GC2, GC-12 or L16’s were cycled using the same cycle life testing as the 12V Group 24, 27, 31 etc. what would that outcome, in cycle life, actually look like? Is it fair to suggest a GC2, GC12 or L16 battery has double to triple the lab cycle life, to 50% DOD, than the 12V 24, 27 & 31 etc. “deep cycles” do?”

A: Senior Battery Engineer – Major US Battery Manufacturer:

“Yes, for packs of equivalent energy content (voltage * capacity) the Golf Car types and L16’s are 2-3 times better than the DC automotive sizes (24, 27 and 31).”

Wow! Straight from the source, golf car batteries are 2-3X better than 12V 24, 27 & 31. These flooded 12V Group 24, 27 & 31 batteries are simply marketed in a rather misleading manner.

To make an even fairer comparison I ran the numbers on a group 24 deep cycle test and a GC2 cycle test, done by the same manufacturer. Both batteries were discharged at approximately 33% of their 20 hour Ah rating, and it can’t get more apples to apples, in terms of comparable testing, than this.

The Group 24 “deep-cycle” delivered just 350 lab cycles and the GC2 golf cart battery delivered 1000 cycles when tested exactly the same way. Both batteries were tested at the same discharge rate, to the same end of life point, yet the golf cart battery delivered 650 more cycles than the 12V Group 24 “deep cycle”.

Let’s go over some terms I’ll be using in this article:

Lab Rated Cycle Life:

This term simply denotes what the battery manufacturer see’s in their own white coat, white glove, laboratory. The batteries are cycled under ideal conditions, and quite often to no industry standardized test across brands. Some might test the battery to BCIS-02 and some to BCIS-07. Some might use the 20 hour discharge rate and some might use the 5 hour or 2 hour rate for cycle life testing.

For what it’s worth some battery makers never even conduct a 20 hour test and instead this data is “calculated” from other tests that take them much less time. The batteries which are most likely to never undergo an actual 20 hour capacity tests? You guessed it “automotive sizes” or Group 24, 27, 31 etc.types.  I am quoting the battery engineer with the “automotive sizes” quote.

Battery testing procedures are guided by the Battery Council International or BCI for short. The problem is there are many different cycle life testing procedures and manufacturers rarely tell you which one they use or are testing to for the specific battery in question.

I was recently at a solar trade show and two of the big gun battery makers referenced in this article were there. I asked each manufacturer to tell me which BCI test standards they used for 12V marine G-24, 27 & 31 batteries vs. golf car or other deep cycle batteries. The answers I got…. BLANK STARES.

One manufacturer then suggested the golf car batteries might be tested at a 2 hour rate and the marine batteries at a different rate. If this is so then the spread between golf cart batteries and 12V deep cycle batteries can grow even wider in the real world. Ouch!!!

Light-cycling batteries are already half of the rated cycles of a golf car type battery and they “may” be being treated with kid gloves to boot when you actually compare testing. At a best case the 12V G-24, 27 & 31 battery might be half the cycles of an actual deep cycle in the lab but they may actually be worse than half the rated cycles depending upon the testing used hence the battery engineers statement of golf car type batteries being 2-3 times better for cycling use.

This is just a sampling of some BCI Tests:

• BCIS-05 – Capacity Testing of Electric Vehicle & Cycling Batteries
• BCIS-06 – Constant Current Cycle Life Testing of Deep Cycle Batteries
• BCIS-07 – Cycle Life Testing of Batteries for Golf Carts
• BCIS-08 – Cycle Life Testing of Deep Cycle Marine/RV Batteries

What tests were used, and the differences between these tests, can result in massive variances, brand to brand, and also in their cycle life claims. This is why it is nearly impossible to use lab cycle life data across brands or manufacturers. Through in-house testing battery manufacturers can produce cycle life data across their own products, based on their own testing.

Remember these lab tests are under ideal conditions and the battery is repeatedly cycled up to full and down to the chosen DOD then back up again, all at controlled temps, discharge rate, re-charge rate, rest times and all back-to-back non-stop with no calendar aging or time to sit at 80% SOC and sulfate. These lab derived numbers have very little meaningful relationship to real world cycling performance.

Out in the real world marine batteries rarely, if ever, deliver even half the lab rated cycles, and there is good reason for this. In general, most boaters can expect 10% to as high as 60% of the lab cycles out in the real world. Some might even do better but on average I see well under 50% of the lab suggestions. The only useful lab data is lab data within a brand or manufacturer of batteries.

For example, if Deka/East Penn says their 6V GC2 golf cart battery is 700-1000 cycles, when compared to their 12V Group 24, 27 or 31 deep cycle, using the same test criteria such as BCI 2, this can be good guidance, and I stress the term guidance. It is only good guidance within the Deka/East Penn brand as to which of their batteries could be expected to deliver the most cycle,s when used in a deep cycling application. However, if Trojan suggests their 12V Group 24, 27 or 31 deep cycle marine battery (SCS-150, SCS-200 & SCS-225) have 600 cycles, you CAN NOT and SHOULD NOT compare that data to another brand or manufacturer. It is beyond meaningless to do so. Remember these companies rarely use independent external labs or standardized cycle life test procedures in direct A to A test scenarios across brands.

Real Word Cycle Life:

This one is almost impossible to nail down other than to say, from years of experience, that the average marine battery won’t usually deliver even half the cycles, in the real world, as they do in the lab. Cut lab numbers in half, at the top end, and you’ll be in better shape expectation wise.

In the real world we have so many factors that inhibit lab like results that it is nearly impossible to get anywhere close to this data. By industry standards a flooded battery is dead when it can no longer deliver 80% of its rated Ah capacity. Will a battery still work beyond this point? Absolutely, and they do, but the catastrophic failure rate, such as an internal short, starts to increases pretty steeply as the rated Ah capacity drops below this 80% figure.

The rate of internal failures I see in marine batteries is highest in 4D & 8D then group 24, 27 & 31 flooded batteries. AGM & GEL much less so but it happens with those too. It also happens in golf car batteries but to a lesser extent than I see it in “automotive” case batteries. Why? I don’t have a good answer other than to point at the separators, lightly built construction/grids etc. and lack of space below the plates. The separators are thicker in industrial batteries than they are in automotive cased flooded batteries. The last few GC2’s and group 24, 27 or 31 batteries I have autopsied showed the separators to be nearly twice as thick in the golf car batteries than they are in the automotive cased batteries.

In a recent survey of “Marine Battery Use” on Sailboatowners.com, more than 1000 sailors responded, a truly exceptional response. 79.5% of responders indicated they cycled their house banks to 50% DOD less than 25 times per year. Stack that data point on-top of the fact that 82% of responders reported less than 6 years of marine battery life and that means the vast majority of boaters are getting less than 150 real world cycles out of their marine batteries… Ouch!

While there was a large spread in cycle life between golf cart and group 24, 27 & 31 type batteries, in terms of longevity, none of these batteries tend get within half the lab ratings. Keep in mind that many of these companies claim 1200 “lab cycles”, as seen right in this article, and yet these batteries are still very often failing in less than 300 cycles of marine deep cycle use. Lab cycle life is simply a fairy tale in the marine space. The lower the lab cycle life number the worse the batteries generally perform in a real world application. Golf and industrial batteries can be murdered too, it just usually takes a bit longer.

Capacity Testing:

Unfortunately we have no widely used or widely avaialble test equipment that can accurately tell us the as-now 20 hour ampere hour capacity. It is a real crap shoot and there are lots of tools that try but all fail miserably, except for an actual 20 hour capacity test, which very few are even willing to pay for.

I do offer physical 20 hour capacity testing for my customers with expensive GEL or AGM batteries, or even expensive industrial flooded batteries, but the testing cost, per battery, for a typical sub $200.00 flooded battery, is simply not realistic. As far as I know I am the only marine electrician in the US offering this type of testing and it is EYE OPENING & SHOCKING to many owners.

*EDIT: I know Charlie Johnson of JTB Marine in Florida & Bill Trayfors of YachtSense in Annapolis have now added the equipment to test for actual Ah capacity.

You can do a capacity test yourself but it involves some set up and equipment that most boat owners may not have on hand. It also requires time and patience to do so..

Dock Talk & Battery Life Gossip:

Owner to owner, dock talk, or dock gossip is essentially as useless as boobs on a bull and not meaningful. It could only be meaningful if you have a baseline for comparison & consistency and everyone used their batteries identically, and we simply don’t. Bottom line, ignore dock talk on battery life and learn how to test your own batteries for their true deliverable Ah capacity.

I have one older customer, a delightful guy, with a beautiful classic little day sailor, he claims consistently & repeatably that he gets “7 years” out of his single 12V deep cycle battery. His basis for a failed battery is when he can no longer power his VHF radio to call the launch. Ouch! He has no motor to start, never needs running lights and uses no electronics, he’s old school and I like that! His batteries are most likely dead by year two but his VHF radio draws so little that he once was able to eek out seven years before it would not even power a brief 2A load to call the launch.

He is a battery murderer yet he does not believe nor understand it because he once had a battery last him seven years powering a VHF radio to call the launch. Flooded batteries are considered dead, by industry standards, when they can no longer deliver 80% of the new Ah capacity or 80Ah for a 100Ah rated battery. Would 80% be dead for powering a VHF radio? Absolutely not. However, in many other applications, for which the battery was intended, it would be in marginal shape at best, and would be more prone to failure.

Interestingly his last replacement battery failed internally at year 3 and became a 10 volt battery instead of 12V. Of course he still gets “7 years” out of his batteries, if you were talking to him on the dock, and he see’s no reason to change his charging or use habits. Of course, cost is not an issue for him, so why should he. I can nearly guarantee that if you were to talk to him today, on the dock, he still gets seven years because it did happen once….

This is a prime example of why dock talk is not meaningful in battery life conversations. If everyone capacity tested their batteries, and was honest about when they hit 80% of rated capacity, then we might have meaningful conversations about battery life. We’d also have a lot of owners saying “holy $hit” my batteries are dead in two years??? (head bonk)

In the real world batteries don’t die naturally, they are murdered by their owners. Here’s some of the how and why with regards to the reasons lab data does not compare to the real world.

What Kills Batteries?

• Chronic “PSOC” Use – Partial State of Charge Operation
• Temperature Abuse- Heat MURDERS BATTERIES, the engine room is the last place any battery should be.
• Poor Charging Practices
• Absorption voltages set too low
• Inadequate absorption voltage duration (under absorbing or premature floaulation)
• Incomplete or Under Charging – Alternator only for mooring sailed boats
• Over Charging – Old school non-smart chargers
• Improper Charging – Poorly designed battery chargers, there are MANY.
• No Temp Compensated Charging – If a battery charges at 14.4V this is max at 77F, not at 90F or 100F plus
• Lack Of Maintenance – Exposed plates sulfate in short order
• Contamination – Happens when batteries are not properly serviced and external contaminates get in
• Improper Flooded Battery Orientation – With respect to sail boats
• Improper Bank Wiring – Poor wiring practices can cause interbank imbalances
• Lack of Proper Equalization Charges –
• Batteries Sitting at Less Than 100% SOC – Especially for for days or weeks

Group 24 & 27 / DC24 & DC27

Here is East Penn data for the Group 24 “deep cycle”, called a DC24 (typo labeled DC25), and the group 27 called the DC27. The East Penn DC-24 and DC-27 are the same exact batteries we call “marine deep cycle” and the same exact batteries West Marine labels as Sea Volt Deep Cycle.

If we compare DC-24 & DC-27’s 80% DOD number of 200 cycles, to the previous chart at 80% DOD, we can see that indeed the golf car, L16, GC12’s etc. are performing in the lab at 2-3 times better, just as the battery engineer stated. East Penn also has data on the golf car and industrial batteries at 90F and even at 90F they still wallop the group 24, 27 & 31’s butts in terms of lab cycle life.

Starting vs. Deep Cycle

Don’t laugh, if I had a dime for every boat I have seen using starting batteries as deep cycle banks I would be much further ahead towards retirement.

What’s the difference?

Starting batteries should not be used for deep cycling, but deep cycle batteries can easily be used for most starting purposes. I use deep cycle batteries for starting on almost all sailboat installations. Why? They last longer and can be called upon for cycling if or when the house bank fails. A small aux diesel engine can be started by even a PWC battery so a decent deep cycle house bank makes easy work of motor starting.

Deep Cycle? Compared To What?

Remember what I said above about start batteries used as house banks? The battery on the far right had been replaced 3 times in 5 years. It was one of two used as the house bank. Why were starting batteries used and replaced like for like? “It’s what the boat builder shipped the boat with, so I replaced them with the same type.”

The three batteries pictured here are all made by Deka / East Penn and all share the identical case despite the internal construction being different. The two on the right are East Penn starting batteries and not even rated for deep cycles.

The battery on the left is the Deka /East Penn DC27 which is then relabeled as a Duracell DC27 and sold through Sam’s Club. This battery is rated at 350 cycles in the lab but the other two carry no cycling rating at all.

With this image it becomes very easy to see how the marketing snakes (guru’s if you must) get away with calling the DC27 a deep cycle battery. Sure, when compared to other Group 27 batteries, with which it shares a case, it is a deeper cycling battery. However when compared to a Golf Cart GC2, L16 etc. etc. or any other actual deep cycle battery it is simply an imposter.

Deep cycle? Compared to what is the question you must ask yourself….

Trojan Has Similar “Light-Cycling” Deep Cycle Batteries

Just so you don’t think I am only picking on West Marine or Deka/East Penn here is Trojan’s line up suitable for boats..

I have installed nearly all the batteries pictured in either recreational or commercial vessels.

Top Row:
The top row are the most popular deep cycle Trojan’s I see installed on cruising vessels. They are the venerable Trojan T105 6V GC2 at 225 Ah’s, and Trojan’s 12V golf cart battery called the J150 at 150Ah’s. If you don’t want to deal with 6V batteries the J150 offers identical cycling performance in a 150Ah 12V case.

Middle Row
These are Trojan’s imposter/pseudo deep cycle 12V marine batteries. They are lab rated at just half the cycle life of the top row and bottom row. Sadly all three rows are marketed as “Deep Cycle”. Is this fair or honest marketing???? You be the judge.

Bottom Row
On the left we have the 12V J185 sweeper/scrubber battery. This is 225 Ah 12V battery at 1200 lab rated cycles. It is double the lab rated cycle life of the 12V marine batteries in the middle row. On the right we have the L16 6V sweeper/scrubber battery. This model is 435 Ah and 1200 lab rated cycles to 50% DOD..

If you have the height, any of the batteries on the top or bottom row are great choices. Also please remember not to compare brand to brand cycle life data, it is guidance only within a brand or manufacturer.

Trojan Cycle Life Data – by Battery Line

Here is Trojan’s lab cycle life chart for their various lines of batteries. Both the venerable T-105 and the Group 24, 27 & 30/31 are considered “Signature Line” products but Trojan specifically breaks out the cycle life of the Group 24, 27 & 30/31 from the T-105 level batteries.

As can be seen the T-105, L16, T-125, T-145 etc. all cross the 50% DOD to lab cycles line at about 1200 cycles and the Group 24, 27 & 31 cross it at about half that or 600 cycles.

Both “Signature Line” groups of batteries get the same deep cycle label but one group delivers just half the cycles in the lab. Same sticker, half the performance…? Fair? Honest?

Let’s compare the *cost of two SCS200 Group 27’s and the cost of two T-105 GC2 batteries.

Group 27 Trojan:

• Two SCS-200 (G27) = 230Ah
• SCS-200 Cost = $187.00 X 2 = $374.00
• Cost per Ah = $1.62
• Cost Per Cycle @ 600 Cycle Lab Rating = .62¢
• Cost Per Cycle @ Half Lab Rating = $1.24

Golf Car / GC2 Trojan

• Two T-105 (GC2) = 225Ah
• T-105 Cost = $129.00 X 2 = $258.00
• Cost Per Ah = $1.15
• Cost Per Cycle @ 1200 Cycle Lab Rating = 22¢
• Cost Per Cycle @ Half Lab Rating = 43¢

*Local cost from our Trojan distributor.

Another Look at Trojan’s Cycle Life

Here is a renewable energy document, solar/off grid is very similar to marine use, from Trojan which once again show the Group 24, 27 & 31 to deliver just half the lab rated cycles when compared to their golf and sweeper scrubber type batteries.

Of interesting note the newish Trojan T-105RE (RE=Renewable Energy) battery that delivers about 400 more lab cycles than the standard T-105.

Here’s the Crown Battery Data

Here is the cycle life data from Crown Battery comparing their Marine Deep Cycle Group 24, 27 & 31 to their golf car / GC2 series.

The Crown Group 24, 27 & 31 deliver 525 lab cycles under BCIS 06 testing and their GC2 series deliver *1050 to 1200 cycles.

*The Crown GC6V is a price competitive 205Ah golf car battery.

Many companies, not just Crown, offer a low Ah (sub 210Ah), what I describe as, “home owner grade” or “condo complex” Golf Car battery to meet a competitive price point. These low Ah GC2 batteries often do not have the same exact cycling capability that a standard golf course grade GC2 battery has.

This 205Ah GC6V is not a battery that a golf course would generally purchase but rather a homeowner in a condo association that allows golf cars. Most all of the GC2 manufacturers offer a price-competitive GC2 battery, but they often don’t have the same cycling capability that a golf course grade GC2 has.

Generally speaking if you purchase a 6V GC2 battery with 210Ah to 225Ah, such as a; Trojan T-105, Deka GC15, Crown CR-235, US Battery US-2200 you’re going to be getting a golf course grade GC2 battery. Going much above 230Ah in a GC2 case means the plates can become uncovered when healing more easily than a standard GC2 battery. They are simply trying to stick more lead in there, and this is fine in a stationary application, but less good on a boat that heals.

Light Cycle vs. Deep Cycle

If you’ve been reading my stuff for any length of time you’ll know I like to look inside things, cut them open and autopsy them. Batteries have not escaped my fascination with power tools.

Right:
On the right we have a 235Ah GC2 6V golf cart battery. There are three cells in total and some nice room in the bottom of the case to catch any shed sulfate (think dead skin cells). The plate separators are a nice heavy rubber-like material. Batteries can occasionally short internally as shed sulfate piles up under the positive and negative plates. Once it builds up enough to touch we now have a cell that self discharges due to contact between a positive and negative plate…. The positive plates on this battery measured 0.121″ or just shy of 1/8″ thick.

Left:
Here we have another re-branded sticker shop Group 24 “Deep Cycle” battery. This one is actually manufactured by Exide and sold as a “Marine Deep Cycle”… Sure, if you say so. (grin)

Wow!!!

“Where’s the beef?”

No, I am not kidding. This photo reminds me of the Wendy’s commercial from the early 80’s with the little old lady asking “Where’s the beef?” Laugh all you want but both of these batteries are sold & marketed as “Deep Cycle”. The only ones laughing are the battery makers, all the way to the bank, with YOUR money. Which one would you rather lay your hard earned money down on….???? Which one do you suppose is really capable of deep cycling…?

One glaring dissimilarity between these two batteries, besides the lack of lead on the 12V Group 24 pseudo deep cycle battery, is that this pseudo battery has very, very minimal room under the plates for any shed sulfate to collect. Also notice how much empty battery case is wasted on-top of the plates?

Big box, hardly any lead, while the golf cart battery is a taller box crammed chock full of lead. Both batteries take up virtually the same amount of floor space or foot print.

The big differences between the 12V deep cycle and the 6V deep cycle are more cycles, less cost per Ah, less cost per cycle. These benefits come at the slight impact of a bit more height to fit the golf cart battery.

If you have the height why would you use a more costly yet inferior product..??

Should a Yugo cost MORE than a Lexus? Would you pay MORE for a Yugo than you would for a Lexus? No, of course not, so why do that with marine batteries?

Plate Thickness:

• *6V GC2 235Ah = 0.121″ or just shy of 1/8″
• *Group 24 12V = 0.0617 or just shy of 1/16″

You actually read that correctly, the golf cart battery is almost double the positive plate thickness! Sometimes a picture is worth a thousand words, this one might be worth 1500…. (grin)

As I say repeatedly to my customers and consult clients;

“Deep cycle is often just a sticker, know what you are buying.”….

What about a “Starting” Battery?

This is one of the very few marine batteries I have replaced due to being chronically over charged. The owner of a center console placed an unregulated 15W solar panel on his T-Top and fed it directly to his East Penn/West Marine starting battery. About 9 weeks later the battery shorted internally due to crumbling plates and refused to start the vessel.

Look at the bottom of the battery case and notice how close the positive & negative plates are to the plastic. When the plates started crumbling, due to chronic over charging, brittle flaking lead fell to the bottom and created an internal short. The end cell, closest to you, was the shorted one according to specific gravity readings.

On the left you can also see how brittle the lead grid/plates had become due to over charging.

Starting vs. Pseudo Deep Cycle

On the left is the starting battery that was destroyed do to unregulated solar charging. On the right is a “light cycling” deep cycle murdered in less than one season by deep cycling, charging with only an automotive type alternator & PSOC use.

The Kirkland (Johnson Controls) “deep cycle” battery (on right) was brand new in May of 2015 (date code) and put into actual service in July. By October the battery was only delivering 28.2 Ah’s from its 115Ah factory rating! This battery was in parallel with a sister battery and both tested nearly identically. Let me sum this up……

THESE ARE NOT DEEP CYCLE BATTERIES!!!!!

Long and short I cut both of them open to expose the internal construction……

The Stickers

Here I’ve flipped the two Group 27 batteries around showing the stickers. I also laid out from L to R the negative plate, positive plate and the separators.

The West Marine battery is one of their highest CCA batteries (cold cranking amps) and the Kirkland is anything but a “deep cycle” battery despite what the BS on the sticker says.

Time & time again we hear how different starting and deep cycle batteries are, and when comparing a true deep cycle product to a starting battery, there are definitely some major differences.

In the case of these two batteries however the construction is more similar than different.

• Plate Separator Envelopes = Same Quality/Virtually Identical
• Negative Plates = Virtually Identical Thickness
• Positive Plates = Virtually Identical Thickness
• Plate Size = Deep Cycle Has Slightly Taller Plates
• Number of Plates = Starting Battery Has One More Plate Pair, Per Cell

“Deep Cycle” Group 27 – Positive Plate Thickness

So how do they compare?

Deep Cycle “stickered” Group 27Battery:

• Slightly Larger Plates (taller)
• 6 pairs of positive & negative plates in each cell
• Positive Plate Thickness = 2.15 mm Thick (0.085″)

Starting Group 27 – Positive Plate Thickness

So how do they compare?

Starting G-27 Battery:

• Slightly Smaller Plates (shorter)
• 7 pairs of positive & negative plates in each cell
• Positive Plate Thickness = 2.20 mm Thick (0.087″)

Let’s break it down;

For years and years all we’ve heard is; “Starting batteries have many more plates & much thinner plates“.

Really? These are actual photos and they certainly don’t agree with the sentiment we’ve been fed?

The plates in this starting battery are actually 0.05 mm thicker than the deep cycle battery. D’oh… While the cells are slightly smaller in physical size they did cram one more positive and negative plate into the starting battery in order to deliver a slightly higher CCA rating.. This hardly qualifies as “many more plates & thinner plates”.

While these two batteries are from different manufacturers they all mislead the consumer. Sure, the plates are taller on the deep cycle but the positive & negative plates are virtually the same exact thickness on the starting battery as they are on the deep cycle.

This “deep cycle” stickered Kirkland battery lasted less than 35 real-world deep cycles. After those 35 cycles it could barely muster 28 Ah’s of accurately tested Ah capacity using lab grade test equipment.

Ask yourself, is this Costco/Kirkland/Johnson Controls battery really a deep cycle battery just because the sticker says so? If you think it is please call me, I have a bridge that’s a killer deal…(wink)

Distributor Level Branding

Many regional battery distributors, or “Sticker Shops” as I call them, re-label batteries to create more market share for a particular brand/manufacturer of battery.. The most often re-labeled batteries for marine use are Deka /East Penn, Johnson Controls, Superior and a few others.

The labels slapped onto batteries are occasionally not at all representative of the battery physically wearing the sticker.

For example I have seen many marine batteries that are actually 4D or 8D starting batteries labeled as either deep cycle or dual purpose. I have also seen 4D & 8D dual purpose batteries labeled as deep cycle.

West Marine is at least honest in their labeling of the Deka / East Penn 4D & 8D flooded batteries and they call them Dual Purpose but you can easily find these batteries re-labeld elsewhere wearing a deep cycle sticker.

Here is a good hint regarding 4D & 8D flooded batteries:

There is only one company I know of building a true “deep cycle” 4D or 8D flooded battery and those are hand made by Dyno Battery up in Washington state. Any other flooded 4D or 8D, no matter what the sticker says, is not a true deep cycle battery. Just because they are big and heavy, don’t be fooled by the sticker.

Regional Distributor “Sticker Shop” Issues:

Not to pick on Ultra Power, which are stickered up by a regional battery distributor, but it appears that when shipments get delayed, or stock gets low, I can occasionally find the same rating / specifications sticker on different batteries made by entirely different manufacturers. Scary stuff!!!!

Back in 2009 I had a customer with two Group 27 “Deep Cycle” Ultra Power EV27 “sticker shop” batteries. One was apparently physically made by Deka / East Penn and the other apparently by Johnson Controls. These batteries (pictured) were in a parallel bank and were flat-ass dead in under 2.5 years.

Despite being different products, manufactured by two different companies, both batteries had the same deep cycle specifications of 110Ah on the Ultra Power sticker. Deka to my knowledge has not manufactured a 110Ah deep cycle Group 27 marine battery.. Odd at best….

Look very closely at these two batteries, bought the same day, at the same vendor and labeled identically. The cases are not even close to the same design, the terminals are different, the handles are different, the caps are different and they are likely not both 110Ah batteries.

Caveat emptor when buying sticker shop batteries!

P.S This installation is not and was not my work!

Distributor Level Mislabeling

Here again we have two batteries wearing the same distributor level specifications, and stickers, but they tested differently, when brand new, and were so far apart as to not even be in the same ball park. Heck based on case identification they don’t even appear to be made by the same manufacturer. Coincidentally the specification stickers suggest they are identical batteries….

Distributor Branding = BUYER BEWARE!!

Deep Cycle 12V Group 24 vs. 6V GC2

Why 6V batteries?

#1 They are more durable than 12V Group 24, 27 & 31 marine batteries because they are designed for the rigors and abuses of rough-riding golf carts. They are simply more robustly built often with better separators and always with more lead and thicker plates. While thicker plates do not always make a battery deep cycle, when talking 6V Golf Cart batteries compared to typical 12V Group 24, 27 & 31 this is a truism.

#2 They have considerably longer cycle life than 12V flooded pseudo deep cycle batteries and even in the real world this tends to translate out to approx one third to double more the life of the average 12V flooded battery.

#3 You can fit more Ah’s in a smaller foot print but they do require some additional height..

#4 Price wins! Ignore the West Marine pricing and shop other places. You’ll see the cost per Ah and per cycle between 12V flooded batteries and GC2 6V golf cart batteries becomes even more apparent. The GC2 230Ah battery pictured at the top of this article can also be purchased as a Duracell EGC2 at about half the Sam’s Club’s in the US. This means $109.00 at Sam’s vs. $199.99 at West Marine. The only difference between these two batteries is the sticker that East Penn installs at the factory.

Take a close look at the foot print these two 6V GC2 batteries take up compared to two Group 24 deep cycle batteries. The only sacrifice you need to make, to get all the benefits of golf cart batteries, on your boat, is a little more height to fit the GC2’s.

Don’t Limit Yourself

Don’t limit yourself to just the typical deep cycle batteries you may find at a chandlery or marine store. This is a 400Ah bank consisting of two Trojan L16 size 6V batteries. While L16’s are much taller than 12V batteries, or even GC2 6V batteries, they take up less foot print. For this owner, he had the height, but not the foot print. These two batteries are sitting where two Group 27’s used to be and he now has 400 Ah’s vs. approx 180 Ah’s in the same exact foot print.

“But RC what if I don’t have the height to fit actual deep cycling batteries?”

There are a few way’s to look at this:

#1 Accept your limitations, accept that the marketing is misleading, and just stick with a premium quality “light cycling” Group 24, 27 or 31 flooded battery such as a Crown, Trojan, US Battery or Deka and replace it when it dies. Rolls actually makes a fairly deep cycle Group 27 & 31, though not quite the same as their GC2’s but closer than most, however they are God awfully expensive.

With good care in a coastal cruising application light cycling batteries can still certainly deliver an acceptable life for the cost outlay. If you practice good battery care you may be able to eek out another 6 months to a year beyond where you are now. Cost is minimal & no modifications. Upgrade cost = $

#2 Move to a premium AGM (Lifeline, Odyssey, Northstar, Firefly) or GEL (Deka, Trojan or Sonnenschein/Prevailer) battery. In the Group 24, 27, 31 4D & 8D both premium AGM and GEL are true deep cycle products.

AGM’s & GEL’s are arguably a bit temperamental in how they are cared for, and charged, and these batteries really need to be installed as a “system“. The charging system upgrade costs can far exceed the cost of the batteries. These batteries are simply too expensive to not install correctly. Done correctly AGM can often approach  & some can exceed 6V GC2 life and GEL’s often exceed it.

Of course, like anything, there are always outliers. You can murder expensive AGM’s & GEL’s just as fast as “light cycling” batteries if the system & use is not done correctly. GEL batteries are pretty much the hands down kings of small case cycle life. The Deka GEL is rated at 1000 cycles. I have a number of GEL banks out there well beyond ten years and one into its 17th as of March 2017. My friend Bruce went around the world TWICE in the same set of GEL batteries. Upgrade cost = $$$$$

#3 If you’re going to be doing some serious cruising, consider relocating your house batteries and fabricate / build a new space for them. You can leave the starting battery as a light cycling type, in the original location, and just revamp the house bank. Upgrade cost = $$

Sometimes when you factor in how long you plan to keep the boat, sticking with light cycling batteries, despite the hit in cycle life, may win the value game.

There are Also 12V Golf Cart Batteries

If you are uncomfortable wiring 6V batteries in series or series/parallel you can always purchase golf car durability in a 12V battery. The battery on the left is a golf car 12V battery. This Duracell GC12 is purposely placed next to a Group 31 12V battery. While it’s certainly taller they will usually fit where a Group 31 did and often a where Group 27 did.

The BCI group size of GC12 is far too often over looked in the marine industry. GC12 batteries are usually between 145Ah and 155Ah in a 12V case/form factor.

GC12 Brands/Models Include:

• Deka / East Penn = GC12 (the Duracell pictured is an East Penn GC12)
• Crown = CR-GC150 or CR-GC155 (Crown’s are very attractively priced)
• Trojan = T1275 or J150
• Interstate = 12VGCUTL
• US Battery = US 12VE XC2 or US12V XC2

Many Ways To Configure Banks

As I mentioned before don’t limit yourself in creating a good deep cycling bank for yourself. The options are almost limitless and even 2V batteries, such as those by Rolls/Surrette are available, These large heavy 2V cells are a true 15+ year battery and are the true Kings of the deep cycle world.

Here we are looking as a SERIES/PARALLEL configuration of four 6V 230Ah GC2 batteries. This yields an effective bank size, in a series/parallel configuration of 460Ah’s at 12V.

SERIES:
When you connect two 6V DC batteries in series, negative terminal of battery #1 to positive terminal of battery #2 you’ve now created a single 12V deep cycle battery.

12V batteries are nothing more than 6 series-wired cells inside a single plastic case. A 6V battery is three series wired cells inside a single plastic case. All you are doing for a 12V bank using 6V batteries is wiring them externally in series.

In SERIES wiring of 6V batteries we ADD VOLTAGE but AMP HOUR capacity stays the same.

SERIES 6V + 6V = 12V

Two 230Ah Batteries In Series = 230Ah’s

PARALLEL:

In Parallel wiring we add AMP HOURS but VOLTAGE stays the same.

PARALLEL 12V + 12V = 12V or 6V+6V = 6V

Two 230Ah Batteries In Parallel = 460Ah’s

SERIES/PARALLEL:
In series parallel (pictured) we wire in series first, to attain desired voltage, then we wire in parallel to gain capacity.

This bank consists of two series wired banks to attain 12V each. These series banks were then paralleled to created a 460Ah house bank.

Series Parallel = Less Than Optimal

While these take off points from the series parallel bank can work, and give you 12V, it is less than ideal. Every battery manufacturer I know of advises against wiring a series parallel bank in this manner.

Don’t Just Take Our Word For It

EnerSys, the inventors of the Odyssey TPPL AGM battery as well as the inventors of the Optima battery, and the leaders in standby back up systems, military applications and other industrial battery applications spells out correct parallel wiring better than I can. When you are wiring series banks in parallel this applies.

Quote = Odyssey/Enersys:

“Parallel Connections:
It is common to have batteries connected in parallel to
achieve a desired amp-hour capacity. This is done by
connecting all the positives to each other and all the
negatives to each other.

Typically the positive and negative leads to the load
are taken from the same battery; usually the leads from
the first battery are used. This is not a good practice.
Instead, a better technique to connect the load is to take
the positive lead from one end of the pack (the first or last
battery) and the negative lead from the other end of the pack.

The two methods are illustrated above. Solid lines and
arrows indicate positive terminals and leads; broken lines
and arrows indicate negative terminals and leads.

In both illustrations, the positive leads are connected to
each other; similarly the negative leads are connected to
each other. The only difference is that in the first illustration
the positive and negative leads to the load come from the
first and last batteries. In the second case, both leads to
the load are tapped from the same battery.

The first schematic is recommended whenever batteries
are hooked up in parallel to increase battery capacity.
With this wiring, all batteries are forced to share both charge
and discharge currents. In contrast, a closer inspection
of the second schematic shows that it is possible for only
the battery whose terminals are tapped to support the load.
Implementing the first schematic eliminates this possibility
and is therefore a better one.”

End quote:

Trojan Parallel Takes Offs

Here is Trojan’s diagram.

This information is out there and easy to find, but from what I see on boats, it is not widely looked at. Optimal battery life in the real world is a complex puzzle. All the small pieces ideally need to fit for the best cycle life..! Wiring your bank, as it should be, is one of those small puzzle pieces…

Series Parallel = Optimal

When wiring a bank for series / parallel you will first want to fit and orient the batteries as they will be physically installed on the boat. You then construct the series jumpers and wire them.

Once you’ve created your series 12V banks you can then wire them in parallel. As explained above, by EnerSys/Odyssey Battery, it is good practice that the loads and all charging inputs be wired from opposite ends or corners of the bank, as shown. This helps keep the bank in better balance throughout its life.

With a series parallel set up the terminals you connect the boat to are those two corners. You do not want to “center tap” with a 6V series or series/parallel bank otherwise you may not have a 12V bank for that circuit..

Final Thoughts:

Can 12V Group 24, 27, 31, 4D & 8D flooded batteries work? Sure, absolutely, and they do in the tens of thousands on boats every day. The question here is of value and are you getting what you paid for, or were sold, when you bought what you thought was a deep cycle battery…?

When a 12V flooded marine “deep cycle” battery is sold for more money, and with half the rated lab cycles, my thinking is a flat out no.

When purchasing house bank deep cycling batteries you should always consider cycle life. This is the part most everyone buying batteries forgets or entirely leaves out of the decision making process.

The battery buying process is not just about Amp Hours and $$$. It’s Ah’s, $$$ and cycle life.

By labeling “light cycling” batteries as deep cycle the battery maker wins because you buy more batteries in a shorter period of time. Do your home work and don’t get bitten by the marketing mumbo-jumbo.

Good luck & happy boating!