The low battery alarm poped up on my dash. When I stoped the car it would not restart. I gave myself a jump and drove to pep boys and bought a new battery. I drove about 200 miles of highway driving with no problem.
Battery gage reading 12v. I pull off the highway and the voltage begins to drop to the point where the low battery light comes back on. by the time i park i cant even roll the window back up with the engine running.


The battery is brand new. I dont think it's the alternator because it let me drive so far on the highway.


WHAT COULD IT BE?

 

Most likely alternator problem. Did you have that checked when you were at Pep Boys? (i don't know for sure if they check them or not). The battery should read around 14.3 while being charged by the alternator driving down the highway or whenever the car is on for a while, so if it was at 12 all the way while on the highway - most likely it was just draining the battery. Again, check the alternator.

 

Agreed.. you should be reading around 14v, not 12v.