Dead Battery

A friends 2003 Nissan 350Z keeps having the battery go dead. After 4 Auto Zone batteries in 7 months she opted for the big bucks Nissan battery with the guarantee that they would take care of her. if the car is driven regularly there is no problem, if it sits for more than 3 days then the battery goes dead. Nissan comes to her house and jumps her off (3 times in the last three months)and Nissan has checked the car and battery and can find nothing wrong. Obviously there is a drain on the battery some where but Nissan can not find the problem. Has anyone out there encountered this same problem and has some idea as to where the problem lies??

A guy with a similar problem with a Mercury Milan got a new radio under warranty to resolve his problem. The battery drain could be lots of things, Nissan should be able to track it down. After a few more jumps they will put a good electronics tech on it and figure it out.