On two occasions, a month apart, I have tried to start my Venza (2010 V6 AWD) only to find the battery dead. Both times the car started with a boost and charged the battery after a 1/2 hr. highway run. Each time this happened the car was taken to a (different) Toyota dealership for a check. Both dealerships came up with the same results. Battery tested good and no drains on the system could be found. After the second test the dealership requested should it happen again, not to boost the car, rather have it towed in to assist in diagnosing. The car was found dead after being parked overnight (once sitting for two days) in a garage. Nothing was left on save items that should shut off when vehicle is turned off, lights on auto, fan blower, radio, heated seats. The only aftermarket item is a trailer hitch installed by Toyota and checked OK. The dome light is set to off even when doors open. Any ideas or similar occurences?