What is the main function of the alternator in a vehicle?

The ALTERNATOR generates electrical power and CHARGES THE BATTERY while the engine runs, supplying electricity to the vehicle's systems. ASVAB Auto Information tests vehicle systems. The STARTER motor cranks the engine to start it (using battery power); the ALTERNATOR then takes over, producing electricity to run the car and recharge the battery. If the alternator fails, the car runs on battery alone until it dies. Knowing the alternator charges the battery and powers electrical systems (vs the starter that starts the engine) is commonly tested.