I just replaced my started in my 1991 Pontiac Montana with a used one, now my battery won't hold a charge! Do I need a new battery or a alternator?
first, try to find out how old the battery is, good batteries will last from 5-7 years, sometimes the date is marked off on the top of the battery. The not holding a charge usually is the sign of a bad battery, if you have an advanced auto or similar place near you they will check the battery and alternator for you for free,hope this helped.
It could be that the battery is good but something else is draining it. With the engine running, the voltage should be 14-14.5 volts. If it is, the alternator is good. With the engine off, the volts should be 12-12.5 volts. If it is, the battery appears good. With a twelve year old vehicle, it's probably the second battery and pretty close to it's end.
tenspeed is referring to what is known as 'parasitic drain' and he is right, did you put something, like some custom audio system or alarm..anything like that in?
Looking for a Used Pontiac in your area?
CarGurus has 17,749 nationwide Pontiac listings starting at $879.