I went out this morning for a quick grocery run and my car turned over slow, but started. The grocery store is only two blocks away. When I got back out to my car it wouldnt start at all. It took about 20 minutes of it hooked up to my girlfriends cavalier to get it to start. On the way home my voltage read 14.9 steady. Does this voltage pretty much rule out the possibility of the alternator? Anything else I should look at before going to buy a $150 battery?