I have not used a gel-cell or an AGM battery, but discharging a lead-acid battery to its 'water' state, that is specific gravity in the range of 1.0xx, is not harmful if only done occasionally, and not allowed to remain in that state for more than a few days. Complete discharge to that state was a method used in the past to recover batteries that had become badly sulfated, but were otherwise believed to recoverable (unfortunately, you didn't know until you tried), but the process works best if the battery has not been standing for too long, or has not been dried out. 'Too long' is not well defined, but more than a month is getting into that category. It is normal for a battery in a low state of charge, below approximately 1.100 specific gravity, to have high resistance and low charging current for several minutes at the start of charging. In a 'normal' (not defective) battery, the current will increase considerably as charging progresses, and is a good sign. After charging for a time, the charging current will decrease, as the specific gravity increases, and the current will/should settle at around 3-4 amps, depending on the battery and the charger. A little more or less is not critical.
If the charging current remains low for several hours, the battery has high resistance, most often the result of sulfation, but plate shedding also will cause it. No charging current after a couple of hours probably indicates an open cell, but in that condition, you wouldn't have any current out, either. You might measure normal terminal voltage with an open cell, but the battery will not supply any current.
Normal or slightly high steady-state charging current and specific gravity that does not rise in one cell typically indicates a shorted cell. Terminal voltage during charging will usually be 'normal' in that situation, but the terminal voltage will drop quickly under a small load.
Also, there is nothing wrong with load-testing, or otherwise loading, a battery that is not fully charged; a load test followed by a charge test is used routinely for testing batteries. Battery testers and the test cycle vary among manufacturers, but the best devices use a load test followed by a charging test, with both current and voltage monitored during both parts of the testing cycle. The current and voltage levels at various points during the test cycle then determine the condition of the battery.
I don't know if this answers any questions, or creates more, but here it is.
Harvester
