I am powering my 48V lawn tractor conversion with four Deka Intimidator
9A31 AGM batteries. I'm using the Soneil SON4812SR 4-stage constant-current
6A 48V charger. It finished the bulk charge at 6A constant current, and
started the float stage which is constant voltage, and it has ramped the
current down to 0.5A at this point.
When I measure the voltages across the individual batteries while charging,
I consistently (across three measurements) get 13.56, 13.93, 13.76, and
13.57 volts. At rest, momentarily after taking them off charge, I get
13.32, 13.33, 13.35, and 13.36 volts respectively. (I know that's not a
true rest state, so I'm not trying to use that to measure SOC.)
A B C D
13.56 13.93 13.76 13.57 (charging)
13.32 13.33 13.35 13.36 (resting)
I find it interesting that the two batteries that have the smallest voltage
drop charging (A and D; within a hundredth of a volt of each other) are the
furthest apart at this momentarily resting voltage. I don't have a mental
model for how batteries providing approximately the same open circuit
voltage have significantly different charge resistance, and particularly
how that difference in charge resistance would be neither directly nor
inversely correlated with open circuit voltage.
The batteries are speced to charge up to 14.6V and float 13.4-13.6 so I
don't think I'm cooking them. But with two in the string outside the
"float" range I obviously need to keep checking them and not leave them on
"float" indefinitely.
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