I have a 96 maxima, that my daughter uses in college. In great shape (< 60K miles!), runs great, but over the last year the battery drains after 2-4 days sitting idle. I've had the Alternator replaced, the Voltage regulator replaced, and a new Battery put in...still doing it! Fine if its driven every day, but after a long weekend...nada. And when I Jump it, I have to leave the leads on for 10 minutes before it will even turn over...dead as a doornail.

I took it to another shop and they guy said he traced it to a faulty BCM (Body Control Module), and that they're no longer manufactured and it would cost $1400 for a new one. Our Mechanic said he removed every input to the BCM except power and still saw the .3 draw. (which would kill a good battery in a few days) When he took away power lead from BCM...parasitic draw disappears
I found a used BCM with exact model number match for $75 on EBay, bought it, had him install it and same thing.

He had > 9 hours into it at this point and said "I didn't fix it so I won't charge you...but I'm giving up" Any ideas what to tell the next mechanic? what to test next?

 

Guy at that shop and your mechanic are idiots but at least he didn't charge you. This is an hour job to fix. Also that BCM is only a $30 parts used here on the org.
A parasitic drain of .3 is huge and shouldn't take much to find. The BCM is a huge circuit that controls a lot of things. You need to pull individual fuses to find the exact circuit.
Do you own a multimeter and do you know how to check for a parasitic drain?

 

The BCM is not going to sleep likely due to a bad door or trunk switch. any past body damage? Unhooking the inputs would show an open switch (open door).

 

Make sure the trunk light isn't staying on. The bcm should go to sleep after all the doors are closed and all interior lights are out.

 

I had the same problem...a little drain..you can test it yourself and you'll see the battery drawing amps when everything should be off.

Since my car never went into "sleep mode" and no lights were left on (also checked the trunk), I just installed a kill all switch that I have to manually switch off if I'm not going to use the car for a few days..i don't travel much so this is not really a bother. I never really found out what was draining my battery.