obrienklm — Have a look at the thread "Disconnecting the 12 v Battery" for quite a lot of information on the current drain from the 12-V battery when the car is "off." It's very low indeed. I assume that you didn't inadvertently leave your car in ACCessory mode by mistake. It's easy to do! If the radio is "off" the only indications that it's in ACC mode are, I think, the fact that the clock display is still "on," and the Start switch still glows amber. It draws quite a high current in this mode (~5 A as I recall), but even this mode powers down after an hour or so (I don't remember the precise time-out offhand). The 12-V battery is a 48 Ah unit, so to run flat in 3 days requires a current drain of ~0.67 A.

Stan

P.S. The 12-V battery does not start the car! This is one of the functions of the high-voltage (NiMH) battery. The 12-V battery powers all the control electronics, lights, gauges, etc. You can't start the car if the 12-V battery is flat because the control electronics don't work. [You also can't start the car if the NiMH battery is too low to crank the engine (via motor-generator #1), even though the 12-V battery is fine.]