My 66lb former group 31 US battery, which was a dual purpose marine flooded battery rated at 630CCA (IIRC) and 130 amp hours, after a regular' full charge, required 6.2 amps to be brought to 16.2v.
When those 6.2 amps tapered to around 4, it usually coincided with specific gravity rrising to 1.275 to 1.285 on all cells, indicating true full charge. the same cells always red slightly lower or higher, AND this exact number would vary depending on teh electrolyte level, Lower when full higher when just above the plates.
But after a while I just waited until amperage tapered to about 4 @16.2 and called it good rather than dipping the hydrometer. As the batttery aged eventually it would not taper to 4 but would instead start rising, and since my power supplies have 40 or more amps to seek/ maintain a voltage this could lead to thermal runaway, but I set my timer for 15 minutes to check things and terminate when required..
It was a weird battery, I got about 500 deep cycles from it before relegating it to shallow cycle duty.
if I had not observed then measured the bottom of one cell getting hot, I might have thought it was 'just fine', and perhaps even 'still going strong'
but evidence proved otherwise. I had watched its voltage rentention declining per AH removed for those 500 cycles and was getting irritated at the ever increasing time and effort it required to return it to a true full charge.
It lasted several years more shallow cycling on workshop floor with much les care and intervention, and still had not shorted a cell when I traded it as a core, and I could still get specific gravity to 1.275, on 5 of the cells anyway, the 6th was 1.250 max, the cell which liked to heat up when charging.
Gassing usually begins around 14.2v, but where it begins and how vigoruously depends on the battery and the rate it gets brought up to the low 14's. Now @ 16.2v, I called that Fizzing, and can smell it 10 meters away if downwind.
If one wears a strong headlight and good eye protection, one can see the different rates of bubbling at different voltage, and watch it occur at different states of charge and amperage and temperature.
gassing is good, it destratifies the electrolyte, mixing it up, helping it to migrate into the depths of the porous cells Long gassing events at high voltages after the battery is fully charged, are not.
Do not trust teh Ammeters on the transformer based chargers, I have a 2 and 10 amp schumacher that says 2 and 10 amps on its ammeter, but in reality is 0.56 amps max on teh 2 amp setting and 4.3 amps on the 10 amp setting.
The battery itself decides how much voltage will be pushed to with a given amperage. Again battery size, temperature, health and state of charge are all variables. So even on a specific battery, it will be different at cycle 5 or week one compared to cycle 150 or week 72.