The battery stores electricity to start the car. It also supplies- when the engine is not running- current for the

• ignition system
• lights
• fan in the heater
• air conditioner
• windshield wipers
• defroster
• radio
• horn

However, if electricity kept flowing out of the battery and never came back in, it would soon be all used up, making the battery dead. Therefore, the battery is connected to the alternator, or generator, which generates electric current. The alternator is turned by the power of the car's engine while it runs. The current made from the alternator flows back to the battery, restoring the power.