I have a three-year old Prius and, on several occasions, the small auxiliary battery has gone flat when the car has been left unattended for two to three weeks. The Toyota service centre has suggested that if I leave the Prius in a locked garage I should leave it unlocked, as the security features do cause a small but significant drain on the battery, but if I followed this advice would my theft insurance be invalidated, and, if so, what else might I do to avoid the original problem?