In order to recharge your car battery while driving you will need to operate the vehicle over 1,000 RPM’s for a sustained period of time. The longer the battery has been dead, the longer it will take to fully recharge it. However, by driving for at least a half an hour at 1,000 RPM’s, you should charge your battery enough that you will be able to restart the vehicle once you turn it off. Driving for an hour, without using the lights, radio or other electrical devices, should fully charge your battery.