Question: what are the causes of a bad alternator?
Answer: Test the Output. When an alternator wears out, it does so in stages. ...  Check the Battery. Many times, the alternator will fail from being "stressed" by a dead or dying battery. ...  Listening for Sounds. Inside the alternator is a rotor that spins on a set of ball bearings. ...  Losing Ground. ...  Belt Slippage.