Hello.

Recently my 1990 Nissan Laurel got a flat battery from leaving the door open for 30~ mins, I called up a mechanic and he checked out my battery and told me my battery was bad, So I took my Heavy Duty battery out of my other car and at the same time I got my alternator checked out (which checked out alright), I put it back together only to find out the same thing happens, The battery still doesn't charge and dies down when running idle. Along with that there is a squeak from the alternator belt which I think would be from over tightening.

Any help with these problems would be greatly Appreciated..

Thanks, David

maybe the alternator need some carbon refill or some cleaning..it happened to me last time i hope its the only problem.

Have the battery itself load-tested to be sure it's up to spec. You might also want to try charging the battery out of the car. You can buy battery chargers that will let you know if the battery is taking a charge properly or not.

As for the alternator, a LOT of the time (I'd even say most of the time) bad alternators will test GOOD. They're very had to "catch." If the battery is good but not taking a charge, I suspect the alternator.

If neither the battery or alternator are bad, you probably have a parasitic drain on the battery somewhere.