I know there are several questions on here about finding the source of a battery drain (like Battery drains by itself when vehicle is parked (parasitic draw) ). However I don't think the answers address my problem.
Occasionally when I go to use my car in the morning, it will have a dead battery. Because it is an intermittent problem (on the order of once every couple of months), it's no surprise that mechanics find nothing when doing an overnight draw test. That is to say that the problem has never occurred when the car is in the shop.
FWIW, I have not left the lights on on the nights that the battery drains. I can't rule out any similarly stupid mistake, but at least its not the lights. Also, we tried the simple step of replacing the battery about 6 months ago. The load tests done by various mechanics never implicated the battery, but we did it anyway.
So my question is, what strategies should I use to track down an intermittent battery draining draw?