why my battery wont stay charge on my 1991 chevy cavalier?

[JAMIE T]

i have a 91 chevy cavalier wagon that my battery wont stay charge but battery and alt. are new i just installed them yesterday while the car is on the volt coming out the battery is around 12.6 but then it starts to go down what else could it be

 

[Fire's Shaddow]

have the alternator checked, especially the rebuilds can be defective from the factory that is probably the case here.

 

[jeepster]

While the engine is running you should have approx 14 volts at the positive side of the battery if you only have 12.6 then your alternator is not putting out check the fuses,re check your installation work, or the new alternator is bad.
If battery volts starts dropping when the engine is off then you have something on that is pulling power or the new battery needs to be replaced.
Just because something is new doesn't mean it works

 

[PARTSMAN]

Timing is everything. Good thing it is the last weekend for cash for clunkers. Time to trade up.

 

[who]

1 problem people never think about is the battery cables corroding up with that greenish scale on the copper wire...it'll eat up all the conductivity to the battery and prevent it from charging.Its a classic problem we all over look. (Electrolisis)could be both cables from the age of it and you'll get better milage and longevity out of it.