One problem related to battery dead has been reported for the 2012 Toyota Sienna. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2012 Toyota Sienna based on all problems reported for the 2012 Sienna.
Brand new vehicle lasted about a week, wife parked car, went into store, came out and van would not start, wife and kids were stranded in rough part of neighboring city, battery dead, Toyota service tested charging system and found nothing wrong, they didn't replaced battery as a precaution.