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.).
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 expire
ment) 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.