In an automobile electrical system, the battery supplies power to the starter motor. The starter rotates the flywheel, and the flywheel turns the crankshaft, which moves the pistons of the engine. The alternator keeps the car battery charged and, subsequently, keeps the electrical system going.
The battery provides the current needed to start and maintain the electrical system. It supplies power to the ignition and fuel systems, which create the combustion that runs the engine. When the driver turns the ignition key, the battery supplies power to the starter motor, which cranks the engine. If the battery is weak, the electrical current it supplies is insufficient to fire the spark plugs and to start or keep the engine running. Although a car can start with a faulty alternator, it cannot run for long since the alternator keeps the battery charged.
The automobile charging system consists of the alternator, regulator and interconnecting wiring. The alternator uses electromagnetism to produce alternating current, using a series of diodes to convert this current into direct current since all modern automobiles use the DC electrical system. The regulator keeps the charging voltage between 13.5 and 14.5 volts to protect the vehicle's electrical components. Most vehicles have a voltmeter that indicates the charging health of the vehicle.