To keep the battery charged and on-board systems running while in operation, our alternators are like a little electrical generator. It is spun by the serpentine belt on your engine and makes electricity. This electricity is used to power the electrical systems required to run your vehicle. It also powers all of your electronic accessories like your stereo, navigation, heated seats and air fans, as well as charging all the electronics you have plugged in.
After the alternator has done all that, any electricity that’s left over is used to charge your battery. You can see where we’re going: if the battery isn’t getting enough electricity to stay charged, the problem may have something to do with the alternator.
Now it could be that the alternator is bad – they do wear out over time. There are a number of failure points within the alternator, but in practice, it costs less to simply replace the alternator than to take it apart and repair it.
Alternators are usually belt driven. The belt turns the wheel and creates energy in a copper coil. The job of the alternator is to transfer that created power back to the battery to run your electrical systems and give you starting power.