The alternator belt is a belt that transfers the engine's rotational energy to the alternator. This belt wraps around a pulley connected to the crankshaft. As the engine starts and the crankshaft rotates, the belt also moves, transferring rotational energy to the alternator. The alternator, which is a type of generator, converts this energy into electricity and charges the battery to supply power to various parts of the car.
Although the primary function of the alternator belt, as the name suggests, is to transfer rotational force from the engine to the alternator, in modern cars both the timing belt and the alternator belt are also responsible for driving other engine components such as the water pump, power steering pump, oil pump, air conditioning compressor, and more.