Can a bad alternator cause a bad battery?
Can a bad alternator cause a bad battery? But, before you condemn it, run a voltage drop test between the alternator and battery. GM typically runs a fusible link wire between them for overload protection and they can go bad, mimicking a bad alternator. A voltage drop of .25 volts or less is Ok and the alternator is bad. Why does the Volt gauge go up and down? The voltage always fluctuates, goes up and down depending on how much current is being used by the accessories, and the engine rpm, the charge state of the battery, the ambient temperate,...