I have had the same problem. occasional drained battery. I called the dealer service andthey said it could be the alternator, I dought that. There were not warnings or faults showing. and it was a couple months between incidences.
I will check the doors and trunk. The trunk does have a motorized pull-down, but maybe if there is a sensor that may be loose or bad ic could happen. if there is a sensor, does any body know where it could be?
Tony