How To Tell If It's My Battery Or Alternator. Turn your car on and let it run. The failures of a battery are.
Check the condition of the battery. How to know if alternator is bad. If the battery is drained or its power is low check to see whether you left the headlights or an interior light on.
If the voltage is significantly lower than that then there could be an issue with the alternator but there could also be an.
If the battery is constantly dying this is a sign of a bad alternator. Without a functioning alternator the vehicle quickly uses up all of the batterys capacity leaving it drained. You can check the alternator by simply starting your car and then disconnecting the negative battery cable. A voltage drop of 5 volts or more means the wire is bad.
