Strange VRLA AGM battery issue

Posted By: pschnahc

Strange VRLA AGM battery issue - 12/05/19 06:20 PM

Greetings BITOG Council, I come seeking your thoughts and advice. 3 weeks ago, I scored a pair of OEM VWAG Varta AGM batteries in H8 form factor with a 105Ah capacity. They were manu'ed in 2017 and sat on a pallet for a couple of years I assume. They will be used in UPS backup service. Now the problem became apparent right off the bat while doing the initial equalization charge. One battery takes a charge well and as the SOC rises so too does the internal resistance and thus the voltage from the 'taper current' charger. Perfectly normal and expected. It also does not heat up. The second battery is the strange one. It will sit there and eat current (low internal resistance) and warm up. Not hot, but rather warm.

Using transformer chargers (taper current), at 2amps, the voltage will not exceed 13-13.1V, and will drop to 12.9V if another AC appliance on the same mains as the charger turns on. At 6amps the battery will not exceed 13.2V. At 10amps the voltage will not exceed 13.8V and at 16amps the voltage will not exceed 14.2V. The battery only warms up. Could this be hard sulfation? A sidebar observation is that when I put the 16amps on it (thus higher voltage), the DVM seems to swing up and down as though plate sulfation was being reversed by it.

Otherwise, that weird battery performs well. It'll take 1400watt loads like a champ, it's resting voltage is pretty normal but it's way too different to be series up with the other one and charged by the UPS. The good ends up near 15V (briefly before i disconnected it) while the weird battery sits at below 13V.
What should I do? I'm leaning towards taking it back and finding a match for the other one, maybe with a closer serial number. Or should I stick it out and try and 'rehabilitate' it. They're brand new batteries so the differences (in chemistry) is surprising.

Posted By: dogememe

Re: Strange VRLA AGM battery issue - 12/05/19 06:30 PM

The one that is getting warm is no good.
Posted By: Chris142

Re: Strange VRLA AGM battery issue - 12/05/19 06:39 PM

They sat too long unused and discharging. Both a junk. Even the one that seems ok wont last long at all.
Posted By: meep

Re: Strange VRLA AGM battery issue - 12/05/19 07:01 PM

I slow, long term true desulfation process might help, but it almost sounds like the sub 13V one has a weak cell. If so, the rest of the cells will be chronically over-charged and will likely not last long.
Posted By: Wolf359

Re: Strange VRLA AGM battery issue - 12/05/19 11:11 PM

Either take it to an auto parts place and get it load tested or get your own load tester. Fully charged no load voltage at 70 degrees is supposed to be 12.7 volts, the no load voltage is after the battery is at rest for a few hours. Can't really tell if it's your charger or the battery. That's why you get it load tested.
Posted By: slybunda

Re: Strange VRLA AGM battery issue - 12/06/19 04:45 PM

Did you charge the battery up to 18v?
Posted By: pschnahc

Re: Strange VRLA AGM battery issue - 12/16/19 10:39 PM

update: yep, the warm battery is no good. Seems fine and probably wouldn't be noticed in a car application (until its too late) but it's gotta go back for sure.

Originally Posted by slybunda
Did you charge the battery up to 18v?

18V? No way! Wouldn't dare go over 15V and then only in a very rare cell-eq regime
Posted By: pschnahc

Re: Strange VRLA AGM battery issue - 12/21/19 04:41 AM

Final Update: Got it switched yesterday, the fella gave me a bit of a hard time because the battery read an OK voltage (12.4) and could pump out the amps on the tester but chalk it up to being an AGM battery. I told him, you try and fully charge this thing and see how fast it gets hot. The other battery never got warm, once. So he agreed, grabbed another one off the pallet, mfg 14th week of 2018, read 12.8V off the pallet which was a great sign. Now we're in business. Got them both EQ charged, topped off and both read 13.2V OCV after 8 hours., Sweet deal! Now time to marry them and not worry for hopefully about ten years.

Posted By: gathermewool

Re: Strange VRLA AGM battery issue - 12/23/19 05:19 PM

How long did you EQ charge them? I’m always very wary of EQ charging too long.
Posted By: pschnahc

Re: Strange VRLA AGM battery issue - 12/24/19 04:07 AM

Only about 20 hours though it wasn't a cell equalization with the high voltage, just a battery eq where I trickle charge the two 12V batteries in parallel before putting them in series for the 24V UPS
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