Equalizing AGM batteries

[rogern]

I've been thinking about running an equalization charge on my 400AH AGM battery bank, with 2 Universal Battery 4D, 200AH batteries. It's no longer providing me with 200 AH before reaching what I believe is a 1/2 discharge voltage of 12.30, 12.35 VDC. I've been aware of Lifeline's "ability" to be equalized, and have read their descriptions of their batteries and why they're equalizable, and can't really see why their AGMs and theirs alone could be equalized. Can someone enlighten me as to why what works on Lifelines can't work on my admittedly cheaper but still commercial grade AGMs?

If there's already been a thread on this subject, I couldn't find it, so would appreciate being pointed in that direction.

Thanks,
RogerN

[Paul L]

Check with the manufacturer. I had some failing Northstar AGMs and they had a procedure to equalize. I think it was primarily to try and avoid warranty claims. The equalization didn't help.

[Maine Sail]

Originally Posted by rogern

I've been thinking about running an equalization charge on my 400AH AGM battery bank, with 2 Universal Battery 4D, 200AH batteries. It's no longer providing me with 200 AH before reaching what I believe is a 1/2 discharge voltage of 12.30, 12.35 VDC. I've been aware of Lifeline's "ability" to be equalized, and have read their descriptions of their batteries and why they're equalizable, and can't really see why their AGMs and theirs alone could be equalized. Can someone enlighten me as to why what works on Lifelines can't work on my admittedly cheaper but still commercial grade AGMs?

If there's already been a thread on this subject, I couldn't find it, so would appreciate being pointed in that direction.

Thanks,
RogerN

Roger,

You can not run a capacity test to half discharge as the curve is not linear so it really tells you little in the whole scheme... Also as batteries age the voltage curve under load can change.

The only really accurate Ah capacity test is to test the batteries at 75-80F at the 20 hour discharge rate of 20A for a 400Ah bank (try to keep the 20A steady as voltage decays). You stop the test at 10.5V, then recharge immediately. Count how many hours it took at 20A before attaining 10.5V and this is your current percentage of the original 20 hour rate. Often times this alone can have a "reforming" effect and restore some lost capacity.

If these are Deka AGM batteries, or some others, they do not advise EQing them but I have seen some improvements holding 14.6V - 14.7V for 24 hours. Not all AGM batteries are created equal and the "premium" brands really are longer lasting and more resistant to the effects of sulfation. Odyssey, Northstar, Firefly and Lifeline are among the best of the AGM's and truly designed for deep cycling. The new Trojan Reliant AGM's will have to be proven over time I guess.

[CharlieJ]

+1 on what Maine Sail said.

[rogern]

Thanks for your always expert opinion. But, my original question remains: why should I not try "equalizing" my 4D AGMs? It sounds like you've experimented with "lesser" AGMs, charging them at 14.6 -14.7V. Have you tried charging them at +15 Volts, and if so, what did you find?
I'm not worried about warranty issues, but obviously don't want to destroy the batteries. Far better to continue to use them until their capacity falls to an unworkable level than to trash them.
Thanks,
Roger

[CharlieJ]

Really, no reason at all not to try and "equalize" them as they are basically toast now. If it were me with the issue, I would use a power supply and the Lifeline process while very closely monitoring the temperature of the batteries as well as the voltage and current at the battery terminals.

[rogern]

Well, they aren't toast yet, they basically seem to have lost about 30AH from their performance when new. I hope I can milk them for at least another year before the lower capacity really becomes too much to live with. We've tried to be really diligent about not discharging them below ~ 12.3V and about getting them recharged within a day and fully recharged within a few days - maybe a week + a couple of times. I just want to do everything I can to keep them reasonably healthy for as long as possible. Hence, my interest in equalizing. The thing is, I've been an electronics tech for a long time, chasing electrons back when we troubleshot down to the component level, and just have a hard time understanding what could make Lifeline AGMs different enough to make them "equalizable" while other AGMs aren't. It seems that their similarities, at least in this regard, would outweigh their differences. But I'm not a battery engineer, so...

[Paul L]

Originally Posted by rogern

Well, they aren't toast yet, they basically seem to have lost about 30AH from their performance when new. I hope I can milk them for at least another year before the lower capacity really becomes too much to live with. We've tried to be really diligent about not discharging them below ~ 12.3V and about getting them recharged within a day and fully recharged within a few days - maybe a week + a couple of times. I just want to do everything I can to keep them reasonably healthy for as long as possible. Hence, my interest in equalizing. The thing is, I've been an electronics tech for a long time, chasing electrons back when we troubleshot down to the component level, and just have a hard time understanding what could make Lifeline AGMs different enough to make them "equalizable" while other AGMs aren't. It seems that their similarities, at least in this regard, would outweigh their differences. But I'm not a battery engineer, so...

Note that Lifeline did not offer up the equalization plan till after they had many issues in the field. As I said earlier why don't you contact the original manufacturer and see if they will give you an equalization procedure. I don't believe Northstar publishes one, but they did give it to the distributor who sold me my (failed) agms.

If you are really only down 30ah, that doesn't sound too bad to me.

[smac999]

I would do a full c20 test as menetioned above first. see where you are at. after recharging, that alone may help the batteries a bit.

I believe my US AGM's say do not exceed 15v

[boatbod]

Generally, equalizing agm batts is a last ditch effort to recover capacity lost due to under charging and sulfation. You may get back some percentage of capacity but it's not going to make them 'new' again. Usually 15.5v for 8hrs.

[rogern]

So, can anyone tell me how to build or where to get an affordable dummy load that I can use to do the test?

[boatbod]

Figure out the appropriate 20hr load and then stack up a bunch of halogen light bulbs to give you that draw. E.g. Automotive headlights

[sailinglegend]

Originally Posted by rogern

So, can anyone tell me how to build or where to get an affordable dummy load that I can use to do the test?

I did a 20 hour test in April. The best way is to do each battery in isolation which means you only need a load of a max of 8-10 amps. This is easy with Nav lights and instruments all switched on, and you can switch on extra small lights as the battery voltage falls to keep the discharge current constant. I also plotted the voltage ever hour on graph paper. With five batteries they all plotted very closely when overlayed on the same graph.

This was a tedious procedure and meant turning the fridge on and off and changing other loads to provide a constant current.

On one of my five batteries I did a "Reserve capacity" test. This tells you how many minutes the battery will last with a discharge current of 25 amps. Useful to know if your car battery stops charging and you need to get home! This is usually commonly quoted for start batteries but even my Lifeline deep cycle AGMs give a a figure of 390 minutes which is a much easier test than a 20 hour discharge. This test was within 5% of my twenty hour tests on the other four batteries. Mine were all around 55-60% and are still going strong.

My first c20 test dropped to 10.5 volts under load after about 12 hours which is 60% of the 20 hour discharge time. My next test was with a c20 discharge rate 60% lower and produce a discharge curve that dropped to 10.5v at 21 hours. Such precision is probably not necessary - you just need to get a rough idea of the capacity, so if your 20 hour discharge test only lasts 15 hours that's a fairly quick test.

A "Reserve Capacity" test could be a much quicker way to get a result.

By the way Lifeline recommend the batteries should be replaced when they reach 50% of their rated capacity.

[meridian28]

It would be less expensive to use 120v incandescent light bulbs instead of halogen.


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[Maine Sail]

Originally Posted by rogern

Thanks for your always expert opinion. But, my original question remains: why should I not try "equalizing" my 4D AGMs? It sounds like you've experimented with "lesser" AGMs, charging them at 14.6 -14.7V. Have you tried charging them at +15 Volts, and if so, what did you find?
I'm not worried about warranty issues, but obviously don't want to destroy the batteries. Far better to continue to use them until their capacity falls to an unworkable level than to trash them.
Thanks,
Roger

Roger,

You've not mentioned a battery brand yet so it is hard to say. Not all AGM batteries are created equal and some are not true deep cycle batteries despite the sticker perhaps suggesting they are. Odyssey & Northstar can be reconditioned/reformed but this is not an EQ charge.

Lifeline batteries are designed and intended to be equalized, valves, case, matt and electrolyte volume are all part of this design.

Other AGM batteries are not designed to handle EQ and plate damage as well as drying them out can occur. I have tried to equalize numerous under capacity East Penn batteries and in each case they got far too hot or did not recover any lost capacity. In a few cases they developed internal shorts within a few weeks of an EQ attempt. I have seen slight improvements in East Penn AGM's by holding absorption voltage or .1V -.2V higher than max suggested for 24 hours. If your batteries were toast, and you'd confirmed this with a C/20 test, I'd say sure go ahead with an EQ, but they don't sound like they are toast and a capacity test has not been done.

A dummy load can be created with a bank of on/off toggle switches, some light-bulbs and socket bases. Resistors are more accurate and can work too especially for the finer .1A - .2A loads. I would not test the bank as a bank because one battery may be performing worse than the other and as a bank you'd not know this...