Batteries sometimes take many hours to recharge; if the battery is severely discharged (12.2 volts or less for associate degree flooded battery) then it should take up to twelve hours or a lot of to recharge. The a lot of discharged that your battery is, the longer it will take to recharge it.
Fast charging isn't suggested, 20-amps or higher than is mostly thought of a quick charge. continual quick charging associate degree automotive battery might overcharge the battery and scale back service life.
To determine however long it'll want recharge your battery, you want to confirm what proportion reserve capability your battery has, so as to calculate the number of amp-hours in an exceedingly battery, the rule of thumb is to multiply the reserve capability.
For that reason, it will simply take twelve hours or a lot of to totally recharge the battery. Even once twelve hours, thanks to the reduced voltage, the battery might need a lot of charging to urge it 100% charged.