What could prevent an alternator from charging a battery?

An alternator may fail to charge a battery due to a defective diode or a broken belt. In the context of an alternator, diodes are crucial for converting the alternating current (AC) generated by the alternator into direct current (DC) that charges the battery. If any of the diodes are defective, the current flow can be disrupted, leading to insufficient or no charging of the battery. Additionally, the belt that drives the alternator is essential as it connects the alternator to the engine. If this belt is broken, the alternator will not rotate and thus will not generate electricity. Therefore, both a defective diode and a broken belt directly impact the alternator’s ability to perform its function of charging the battery.

While low battery fluid levels, overcharging issues, and faulty spark plugs can affect the electrical system of a vehicle, they do not directly cause the alternator to fail in its primary role of charging the battery.