Occasional flat 12v battery - garage confirmed no problem and no lights left on. Could it be that too much use on the double locking door system together with not enough running the vehicle to charge the battery? This seems the only solution because the vehicle is often taken out of the garage parked outside and locked, then later returned to the garage without starting the petrol engine. Above is a friends 2006 Prius, I have a 2007 model and do not have this problem. We also know several other owners of Prius who have not had this problem - has anyone had this problem, if not are my assumptions correct? David Harrison UK.