Five main functions of an alternator:
1. Charges the battery: Replenishes the battery’s power while the engine runs.
2. Supplies electricity: Provides electrical power to the vehicle’s electrical systems.
3. Powers accessories: Supplies electricity to headlights, radio, air conditioning and dashboard systems.
4. Maintains battery voltage: Helps keep the vehicle’s electrical system at the correct operating voltage.
5. Supports engine operation.
Signs of a bad alternator
1 Battery warning light appears on the dashboard.
2 Headlights become dim or flicker.
3 Difficulty starting the vehicle.
4 Battery repeatedly goes flat.
5 Strange whining or grinding noises.
In summary: An alternator must be changed when it can no longer supply sufficient electricity or maintain the correct battery charging voltage.