My experience to date......have left the HiHy unused for up to 2 weeks with no problem starting. 99% of use is around town with trips averaging less than 10 miles each. Base 2006 HiHy 4WD. If I were in your position I would suspect some current drain when turned off is draining the 12v battery. The alternative I would suspect is a bad 12v battery. Do you know anyone that could measure current drain when turned off....possibly see what the dealer can find. Hope this helps....