Trouble shooting AGM battery

[Pelagic]

My 2009 12V Fulriver 8D AGM 260AH batteries have been disconnected for the last 3 years while I was called away in the middle of a refit for other things

Testing them I found them all at about 11.8 Volts and as my charging system is 24V, I have been charging them in pairs and monitoring recovery.

3 pairs have responded well charging up to 28.6V and holding at 26.4V as before

However, on the last pair , one battery has been getting quite hot on one side only (in line with the + post)

Could this be a Sulfation problem on the AGM or do I have a bad cell?

Can you Equalize an AGM Battery?

[GordMay]

Why would you want to shoot your battery?
Notwithstanding, it shouldn't be too difficult, as they usually just sit there.

Yes,you can equalize an AGM battery.
“... Conditioning/Equalizing Charge: 15.5 volts for 8 hours
Conditioning/equalizing should only be done when the battery is showing symptoms of capacity loss. If conditioning/equalizing is necessary, first go through the normal charge cycle. Once the battery is as fully charged as possible, start the conditioning/equalizing charge...”
➥ http://www.lifelinebatteries.com/manual.php

[Pelagic]

Things Gord..... carefull....I understand they sometimes shoot the messenger...

[BriaF]

I would strongly suspect a dead cell
If you do equalise closely monitor the temp

[roland stockham]

From the heat sounds more like a short than sulfation, likely it is also taking a lot of current at a low voltage and the voltage is not going up during charging as you would expect.

[Tx J]

Originally Posted by Pelagic

My 2009 12V Fulriver 8D AGM 260AH batteries have been disconnected for the last 3 years while I was called away in the middle of a refit for other things

Testing them I found them all at about 11.8 Volts and as my charging system is 24V, I have been charging them in pairs and monitoring recovery.

3 pairs have responded well charging up to 28.6V and holding at 26.4V as before

However, on the last pair , one battery has been getting quite hot on one side only (in line with the + post)

Could this be a Sulfation problem on the AGM or do I have a bad cell?

Can you Equalize an AGM Battery?

I'd pull and replace that one battery that is "getting quite hot" before pushing it any more.
That AGM is a sealed VRLA (valve regulated lead acid) recombinant (normally no outgassing or loss of electrolyte components) electrolyte type battery.
The valve is designed to only open with an overpressure condition, never in normal cycling.
That battery likely has a major internal fault (like a short, or evaporated electrolyte from the mat(s) near the hot spot-lost to a case crack, etc.).

The overheating is likely a preliminary sign of a developing thermal runaway condition (potentially very dangerous).
If the regulating valve has clogged up, you might be looking at an explosive exothermic reaction there, as the remaining electrolyte components decompose inside and greatly overpressure the case. The resulting explosion would probably be pretty energetic.

You didn't give any voltage or current readings for the bad batt, but they are probably somewhat different than the others.
If you want to 'experiment' (or expirement) with it further, trying to get it to recover, safely isolate it and wear a lot of protective gear...

AGM's can be very carefully, rarely equalized, but it shouldn't be necessary normally with a vigorous usual charging regime.
Others far more expert than moi have written about them here a lot.

[Pelagic]

Thanks TxJ this is my first set of AGM and the first problem experienced
Of the 8 ..I identified 2 that had only 11.4 volt readings after sitting uncharged for over 2 years.
They turned out to be the ones that had individual cells get hot... (One just slightly warm)
so I took them offline todayand am slowly charging the remaining 6 (in pairs)and monitoring temps.

Do the AGM experts consider those bad 2 now garbage ..or is there any chance of recovery via careful equalization?
Understandable nervous about sealed batteries

[HappyMdRSailor]

Originally Posted by Pelagic

Thanks TxJ this is my first set of AGM and the first problem experienced
Of the 8 ..I identified 2 that had only 11.4 volt readings after sitting uncharged for over 2 years.
They turned out to be the ones that had individual cells get hot... (One just slightly warm)
so I took them offline todayand am slowly charging the remaining 6 (in pairs)and monitoring temps.

Do the AGM experts consider those bad 2 now garbage ..or is there any chance of recovery via careful equalization?
Understandable nervous about sealed batteries

WOWZA...

And I thought I had a large house... 4 - 8D, not including the thruster windlass pair and start & gen sets...

Almost 2k AH huh???

Watching and learning as I think mine went south/I killed them, even trying to be diligent and caring...

[four winds]

I had two group 31 west marine. About 7 years old when one holed the case under the positive post before noticing. Started checking for the other to do the same and noticed the shore charger never showed the green(ready) light after a day on shore power.

Sure enough the case was warm. Took it mean the same fate awaited the second and it was a failure mode.

Beacause of age just considered it was time.