The amount of time necessary to recharge a 12-volt battery is mostly determined by the battery’s energy level. A severely depleted battery may take up to 12 hours to fully recharge. The most efficient battery chargers are three-stage automatic 12-volt battery chargers.
It is advisable to charge batteries gently rather than hastily. Over time, repeated rapid charging of 12-volt batteries may diminish battery life. Ten amps is considered a moderate charge, while twenty amps or more is considered a quick charge. Fully charged twelve-volt batteries have six cells, each of which provides 2.1 volts for a total of 12.6 volts.