Hi,
It could be a larger than normal parasitic drain across the diode/triode of the alternator. Get a isolator switch temporarly installed like this.
http://shop.advanceautoparts.com/webapp ... tor+switchThen place a fluke/ammeter across the lugs of this switch and turn the car off and lock the doors. (make the hood switch closed if it has one) hood still open. You can make the door switches closed in the lock assembly too while keeping drivers door open.
Now with car locked and asleep, switch the isolator off (ammeter still hooked across lugs). and you will see what it's drawing. Should see 50-150ma, but no more. If you can light a 12v light bulb across the lugs, something is drawing current.
You can now check voltage at fuses, and relays and systematically remove active fuses while watching ammeter for changes.
Body control modules and alarm systems that don't go to sleep can kill batteries. Dual battery cars can also have a 2nd bad battery (like touaregs - I have 3 of them). Sometime you can lock your car from the passengers side and close door and vehicle is locked without alarm system constantly polling and drawing current. A bad alternator is just that, and will back-feed too much current thru the diode/triod (easy check is to unplug the 12v lead).
Jeff