alternators work in conjunction with the battery to produce power for the electrical parts of the car. alternators function by turning the mechanical action of the car’s turning drive shaft into electricity. They do this through the use of rapidly-spinning magnets. This magnetic field in turn produces an electrical current, which is used to power the car electrics. The alternator is also essential for re-charging the car battery, ready to provide the spark necessary to start the car next time.
Alternators are generally quite small in size (a similar size to a roll of toilet paper) don't weigh much and are usually located at the front of the engine.
Usually most modern alternators are maintenance-free and may have a lifespan of a decade or more. Eventually, however, these rapidly-moving car parts start to wear out, made worse over time by dirt and extremes of heat and cold. At best you might experience lights that dim sometimes, or warning lights temporarily flashing on your dashboard. More seriously, a battery that is not being fully charged during motion may mean that your car is difficult to start, or that the ignition fails completely.
In some cases, such problems are put down to an older battery, but more often than not the real culprit is the alternator which is not successfully charging the battery. Check the voltage on your car which should be around 14 volts. Anything less than this and it is likely that the alternator is worn out and will need replacing.