You may think that the battery powers the electrics in your car, but that's not the case. The battery provides electricity needed for the starter motor to start the car. When the car is running, the alternator generates energy to feed the electrical system and charge the battery. The alternator used to be called a generator, and it works in a similar way. In this case, a car's internal combustion engine spins pulleys under the bonnet, which turns the pulley on the alternator and creates energy.