Take it to an electrical shop where they rebuild alternators and let them test it and the the battery. Just because its new doesnt mean a thing. Battery could have a dead cell or a diode burned out in the alternator. It is probably remanufactured so there you go. I dont trust the auto parts store because alot of time employee doesnt know what he is doing or whats good or not good.
January, 28, 2011 AT 6:10 AM
Mirico, just wanted to let you know that I have replaced the battery on my 1990 4dr Mazda Protege with, one new and two others that showed to be good. The alternator was replaced with a new Bosch alternator once about two years ago, and has subsequently been changed two more times with new lifetime warranty Bosch alternators as well. The car is doing exactly what you described. It can sit for several days and start perfectly. If the battery has discharged at all the battery shows to be charging and the alternator is putting out fine and will fully recharge the battery. As long as it sits there it runs fine and the voltage makes no remarkable changes; UNTIL you turn on the headlights or turn on the blower fan. One other thing that it will do is even if you do not turn on the lights or blower but instead take it down the road it will go about 2 miles and be completely discharged and will rapidly die. I am still working on the problem. I am thinking of changing the complete engine wiring harness, at least that is what a few of my mechanic friends thought might solve the problem. If you know what fixed yours I would sure like a response from you or anyone else with this problem.