If you call it a generator or an alternator, they both do the same thing. They will charge the twelve-volt battery while the engine is running and provide power to the vehicle while you drive to your destination. There is a 90% chance you need an alternator if the battery light is illuminated on the dash while the engine is idling. Make sure the drive belt is checked and confirm that it is operating as design. Confirm that the drive belt or serpentine belt travels around every pulley and the alternator by way of the harmonic balancer or the crankshaft.