Lead acid chargers do weird things.
Some will hold absorption voltage for X amount of time, then flash the green light and drop to float voltage.
X amount of time does is a general guess, determined by bean counter joe and Lawyer steve, as what will be safest for the average dimwitted consumer.
Safest being an intentional undercharge for a guy who just wants his car to start in the morning.
Another charger might hold absorption voltage until amps taper to X amount, or perhaps stop tapering, and or when a certain amount of time has passed.
The green light does not mean the battery is fully charged, only that the charger has decided to quit holding absorption voltage, and revert to Float voltage.
If one had a well cycled flooded lead acid, and were to remove the caps, and use a hydrometer on each of the 6 cells, they will likely find that few cells are actually in the green, 1.265+ range, despite the chargers green light.
One might then try to restart said charger, but surface charge voltage which can last for hours, or days, would have charger see 12.7+ volts, and immediately flash green light and revert to float voltage.
One needs to load tge batterybuntil voltage drops to 12.6v, or less, then restart charger, then remove load.
The charger then might hold absorption voltage firvanother hour and specific gravity might creep up towards the 1.275 zone.
But likely not.
Getting 1.275 on all 6 cells can take many more hours held at absorption voltage and often absorption voltage will never do it, and one needs to go as high as 16v, and ‘boil’ the electrolyte.
This can be called Equalization, and is not farvdifferent from balancing lithium, if one were ok with overchargingbthe good cells to get the weak cells to catch up.
Getting SG up to spec on all 6 cells will have the battery perform noticeably better.
One cannot check SG on AGM, so one needs to monitor amperage.
When amps Taper to 0.5 PER 100 AH of capacity when held at 14.4 to 14.7v, then one can say the battery is fully charged.
one cannot determine full charge at lesser voltages.
Most AGMs cant be safely ‘equalized’, according to most sources.
The savvy LA AGM battery nerd knows the asterix’s involved and can accomplish the ‘impossible’
Overvolting an agm can be a very bad idea.
I found best results in restoringbtheir maximum potential performance and capacity by draggingbthem down to 10.5v relatively quickly, then high amp recharging them to absorption voltage, then holding them atcabsorption voltage until amps taper to 0.5 per 100ah, or stop tapering,vtgen float for 12 hours.
If amps start rising at absorption voltage quit charging immediately, and start shopping for battery deals.
120f /48 c is the no go zone.
Getting any ‘garage’ charger to actually fully charge well used deep cycling lead acids, is practically impossible.
A lesson in Futility.
