Truth about Lead Acid Battery Capacity

[Alloy]

Back in 2016 I load tested two expensive 6V(red cases) 250Ah AGM batteries at 12A (20 hour rating).

The test was run over and and over and over and each time the results were the same.

Batteries were charged (using a temp sensor) @ 15.2V (mfg. recommended) bulk and 14.1 float
Resting voltage 12.82V.
12amp load is connected. Voltage dropped to 12.33V.
1 hour later the voltage was 12.32V
2 hours later the voltage was 12.25V
3 hours later the voltage was 12.16V
3 1/2 hours later the voltage was 12.09V and the 12A load was disconnected
4 1/2 hours later the resting voltage was 12.32V

The AGM batteries where returned to the dealer. The dealer tested the batteries and found nothing wrong.

I ended up going with FLA.

 

[john61ct]

Yes, FLA is much better value, and

all manufacturers choose cap test conditions that yield at least 10-20% higher Ah rating at 20hr rate than you will ever see DIY testing yourself

and 30+% higher than you get at IRL discharge rates.

The bottom voltage for lead at 12Vnom is 10.5V, which is only for rare benchmark testing, that will murder any model if done frequently.

Only a precise CC dummy load will yield accurate results.

No matter what, the battery units **must** be of good build quality and properly designed for true deep cycling usage, in order to get decent longevity.

There are only three NA makers meeting that standard for AGM, two for GEL, and maybe a half dozen for FLA.

…

The best battery value by far is Duracell (actually Deka/East Penn) FLA deep cycle golf cart batteries, 2x6V, around $200 per 200+AH @12V pair from BatteriesPlus or Sam's Club.

NAPA relabels it here: https://www.napaonline.com/en/p/NBP8144

Deka self-labeled also sold at Lowes.

None of the others are sold in consumer retail or automotive channels.

 

[RDinNHand AZ]

Good reply. I prefer to test (seldom) with a SOC meter (which have become much cheaper recently) as voltage to SOC is non-linear. I have used the Sam’s Club Deka/East Penn FLA’s with great satisfaction over 5-8 years service and minimal capacity loss. Unfortunately for reporting here I gave the hand written test data to the new owner.

 

[Alloy]

Yes, FLA is much better value, and

all manufacturers choose cap test conditions that yield at least 10-20% higher Ah rating at 20hr rate than you will ever see DIY testing yourself

and 30+% higher than you get at IRL discharge rates.

The bottom voltage for lead at 12Vnom is 10.5V, which is only for rare benchmark testing, that will murder any model if done frequently.

AGM numbers are worse than 30%. I'd pulled 42Ah to reach 50% on AGMs that should provide 125Ah to 50%. Numbers are more like 60% off.

With the 880Ah FLA bank I have now I cheat by using 400Ah in the battery monitor so the SOC will relate to the battery voltage.

I always thought the FLA/AGM numbers were off by 10-15% and I'd screwd the load test up. Turns out the load test was right.

 

[john61ct]

Certainly to be expected from the usual units fraudulently labeled as "deep cycling" at big box retail, the nonsensical "marine" even more so.

Since EoL is supposed to be 80% SoH, do not expect them to last long.

But even the top shelf makers

whose units can last well over a decade if properly cared for

are very hard to get results within 90% of nameplate rating Ah.

 

[Alloy]

Certainly to be expected from the usual units fraudulently labeled as "deep cycling" at big box retail, the nonsensical "marine" even more so.

Since EoL is supposed to be 80% SoH, do not expect them to last long.

But even the top shelf makers

whose units can last well over a decade if properly cared for

are very hard to get results within 90% of nameplate rating Ah.

My FLA are top shelf FLA, Crown CR-235s that were closer to 60% vs. 90%. They'll last 10 years if 10% of the labeled capacity is OK.

 

[john61ct]

My FLA are top shelf FLA, Crown CR-235s

Yes Crown is indeed a top maker of true Deep Cycle batteries, and that model is of the right batt type

Congrats and a great start.

Best way to measure age / wear, is a very standardized benchmark that gets repeated in exactly the same way, same C-rate strictly controlled CC load, same temperature e.g. 77°.

First one - since nameplate Ah is hard to replicate - just after the breaking-in period, during which actual capacity rises a bit

and then every (say) 50 cycles, compared against the first one to derive SoH%.

Time to replace for mission critical professional use is 80% SoH

Non-critical use, can push that to 70% if replacing proactively

So yes a decade is very possible if very well coddled - often at 100% Full as per endAmps, rarely sitting at PSOC, water always topped up

but likely not still above 70% SoH at the 10-year point, of course many captains just keep going until gross symptoms appear.

> that were closer to 60% vs. 90%. They'll last 10 years if 10% of the labeled capacity is OK

That last I'm not grokking but that's OK...

 

[67cj5]

My 115Ah Batteries are over 4 years old now and still hold 13.4+V after 24 hours after coming off charge,

The reason being is how you charge them, Using a normal Charger will bring them close to being fully charged but when you discharge them slowly and charge them normally sulphids build up on the plates and as time goes on the voltage after 24hrs from coming off the charger the voltage gets lower and lower, To stop this you need to let the Charge Voltage sit around 14.8v for 3 or 4 hours at the end on charging and then just to make sure I then hook up the big Noco 26A Charger and it will Pulse and condition the batteries, After that I switch it to the repair mode and then it will make the batteries So they then hold around 13.4V+ for 24 hours and after 72 hours they are still reading around 13.32V,

If you want to desulphid any FLA then run the voltage up to 14.8-14.9v for 3 or 4 hours and then run the Noco Repair Mode and do that once every two or 3 months, This also boosts the CCA up to about 15% higher than the Claimed CCA printed on the Batteries. My 800CCA batteries have given readings of up to 921CCA+ with proper care,

After being 8 or 9 days off the charger my Batteries are reading 13.262v. So it does work.

 

[john61ct]

Good chargers are user custom adjustable.

Different make/models profiles can vary a lot

You should be working off the spec sheet from the mfg, or call in to their tech support if needed.

The key to get to full, is to adjust the AHT Absorb Hold Time (CV stage)

until trailing amps fall to the endAmps spec

often 0.005C, or half an amp per 100Ah.

Going too long will lose electrolyte, NP for FLA long as you're checking

but sealed VRLA units like GEL and AGM can get murdered early in extreme cases.

Part of why we say they are fussier to take care of than FLA

 

[67cj5]

Good chargers are user custom adjustable.

Different make/models profiles can vary a lot

You should be working off the spec sheet from the mfg, or call in to their tech support if needed.

The key to get to full, is to adjust the AHT Absorb Hold Time (CV stage)

until trailing amps fall to the endAmps spec

often 0.005C, or half an amp per 100Ah.

Going too long will lose electrolyte, NP for FLA long as you're checking

but sealed VRLA units like GEL and AGM can get murdered early in extreme cases.

Part of why we say they are fussier to take care of than FLA

Mine are sealed FLA, They claim 600 cycles running them down to 30% SOC but I have never taken them that low, I always recharge them when they get to 50%, They are holding up pretty well and they are 4 and a half years old now. +/- I bought them in July 2017.

 

[Martinjmpr]

IME for a TRUCK, the advantage of the AGM is no need to add water, no need to worry about leaks, etc. Given that most modern trucks seem to come with AGM batteries from the factory, replacing with another AGM seems to be a reasonable thing to do, even given the higher price of AGM batteries relative to FLA.

OTOH, for a camper or trailer, something that doesn't permanently stay in the vehicle, my cheap-****** response is to use FLA just for the bang-to-buck ratio. Our trailer uses 2 x 6v duracell FLA's wired in series and my home-built "power pack" is a Group 27 FLA in a trolling motor box to power the fridge and also charge electronics or run a small (150w) inverter if needed (usually to recharge something.)

I looked into AGM 6v batteries for the trailer but the cost just didn't seem to be justifiable to me. Ditto for the power box that rides in my truck: An AGM would have been at least $100 - $150 more for the same number of AH. Not worth it to me.

And we always have someone in our camping group asking about Lithium. I see zero advantage to offset the enormous costs of lithium battery for a battery pack that's going to be attached to a 3600+ lb trailer anyway. It's not like saving a hundred pounds of battery is going to really offer any great advantage, certainly not enough to justify paying something like $800 more compared to the cost of a FLA with the same capacity.

 

[john61ct]

Just to clarify terminology,

FLA should only be used to refer to units where the electrolyte fluid is accessible for analysis and topping up.

In NA proper lead deep cycling units only come in FLA and VRLA (aka AGM and GEL)

Sealed that are not VRLA, which are not true deep cycling, can be referred to as SRLA.

...

MaineSail has a good rant here

What is a Deep Cycle Battery? - Marine How To

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

marinehowto.com

 

[67cj5]

Just to clarify terminology,

FLA should only be used to refer to units where the electrolyte fluid is accessible for analysis and topping up.

In NA proper lead deep cycling units only come in FLA and VRLA (aka AGM and GEL)

Sealed that are not VRLA, which are not true deep cycling, can be referred to as SRLA.

...

MaineSail has a good rant here

What is a Deep Cycle Battery? - Marine How To

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

marinehowto.com

Mine are Duel Purpose Deep Cycle Batteries which are sealed made for Motorhome use.

Which are 115Ah / 800cca.

 

[Alloy]

Yes Crown is indeed a top maker of true Deep Cycle batteries, and that model is of the right batt type

Congrats and a great start.

Best way to measure age / wear, is a very standardized benchmark that gets repeated in exactly the same way, same C-rate strictly controlled CC load, same temperature e.g. 77°.

First one - since nameplate Ah is hard to replicate - just after the breaking-in period, during which actual capacity rises a bit

and then every (say) 50 cycles, compared against the first one to derive SoH%.

Time to replace for mission critical professional use is 80% SoH

Non-critical use, can push that to 70% if replacing proactively

So yes a decade is very possible if very well coddled - often at 100% Full as per endAmps, rarely sitting at PSOC, water always topped up

but likely not still above 70% SoH at the 10-year point, of course many captains just keep going until gross symptoms appear.

> that were closer to 60% vs. 90%. They'll last 10 years if 10% of the labeled capacity is OK

That last I'm not grokking but that's OK...

Did you wtach the video? None of the FLA/AGM meet your 80% professional or 70% non critical SOC when brand new so there's no way they'll do it after 10 years.

 

[Alloy]

Mine are Duel Purpose Deep Cycle Batteries which are sealed made for Motorhome use.

Which are 115Ah / 800cca.

Dual purpose batteries are like tires that are made to use when it's 110F in the summer and 20F in the winter.