1) How much current (amps) from the alternator is diverted to the battery to charge
2) How long the current is available (drive time)
Generally, running the engine at idle or short stop-and-go trips, during bad weather at night, will not recharge the battery effectively.
In the following situations, the alternator will not adequately recharge a battery:
1. The battery is
drained because an interior light was left on in the car for 18-24 hours
2. The battery is drained because the vehicle has not been driven for a month or more
3. The car is only driven at 35 miles per hour to a nearby store and back 2 or 3 days a week