i know this is not a magna related question but this has got me stumped, Ive got a 89 Nissan pathfinder and if you leave the car and not start of for a week the battery is dead, (battery works fine in my magna). take the known good battery out of my magna and put it into the pathfinder it goes flat. Ive check the interior light and it stays off, what else could it be??

Go get a DC Clamp Tong Ammeter, and wrap it around the positive battery terminal wire. See how much is being pulled from the battery. Then you start pulling fuses, one at a time, until the ammeter shows less current being pulled, and then you'd know what circuit is pulling the current!

Check that the boot light or brake lights don't stay on when you turn the car off. Feel the alternator. If it is getting warm/hot all by itelf one of the diodes has gone and is sucking juice.

Certain small flashing alarm lights can drain a battery within no time.

Go get a DC Clamp Tong Ammeter, and wrap it around the positive battery terminal wire. See how much is being pulled from the battery. Then you start pulling fuses, one at a time, until the ammeter shows less current being pulled, and then you'd know what circuit is pulling the current!

That's a brilliant idea lol

or you can use any automotive multimeter aswell stick the neg lead of the meter on the battery terminal itself, and the red lead on the positive terminal wire. same deal, although the inductive clamp method is alot easier.