The starter, the first part of the engine to turn over, is the small motor that starts the engine. The alternator is the power generator. The battery cannot supply a sufficient amount of power to all of the electrical components in an automobile, so the alternator is indispensable.

The alternator and the starter may fail if they are exposed to excessive severe environmental conditions or if they are subjected to excessive severe operating conditions. However, when it does, often only one part within the alternator has a problem, such as corroded electrodes or sliding parts worn from exposure to water. The alternator can be made to work like new simply by replacing just the parts that are broken or worn this is the idea behind rebuilt components.