How long it takes a car battery to recharge is based on a number of variables that dictate likely recharge time.
A car battery needs to have enough internal cold cranking amps to turn the motor on when the ignition is activated. Cold cranking amps describe the initial output of power when the car is off.
Most batteries today are designed to last about five years under normal driving conditions, depending on the quality and warranty. Corroded terminals and cables which might inhibit the ability of the alternator to charge the battery while the motor is running can adversely affect the lifespan of your battery. A bad alternator is another cause of a battery failure, as is leaving your lights or radio on while the motor is off. These things gradually drain life from the battery and could lead to the need for a jump-start to get your car running again.
Most batteries today are considered maintenance-free, meaning there is no need to add water to the battery cells to extend their life. If you have a maintenance-type battery be certain to use distilled water when refilling depleted cells. Damage to the battery cells can also lead to increased charging required or the inability of a battery to be recharged.
If your battery has been fully depleted, say because the alternator has failed, damage to the internal cells can occur. The alternator is not designed to fully recharge a battery to maximum, but can provide enough charge for the battery to produce enough internal cold cranking amps to start the motor the next time.
Most battery charges have a number of settings and options dictating how much charge the battery will receive over what period of time. The voltage setting should be at 12 volts for an automobile battery unless otherwise specified on the battery label.
The amp setting is most important. The lower the amp setting the longer it will take the battery to recharge. A low setting in amps is called a trickle charge. This setting is good for batteries in vehicles which sit unused for extended periods of time, such as a camper or RV. These types of batteries can benefit greatly from a trickle charge prior to being used. A medium amp setting will slightly shorten the time it takes to recharge a battery, depending on how dead it is. A 10 amp charge could take 40 minutes to a couple hours to recharge the battery.
Most quality battery chargers have a “start” setting which can be used to jump-start the battery. You can likely charge the battery very quickly using this method, at least enough to get the vehicle started. Then be certain to let the vehicle run for a period of time to allow the battery to further charge before turning it off and trying to start it again.
If the battery is just depleted and there has been no damage to the casing or the battery cells, a high amp setting can likely charge your battery in a matter of hours. Any battery that has been completely charged should be left on a trickle charge overnight in order to restore a full charge.