general problems of the 2007 Toyota Avalon

2007 Toyota Avalon [xxx], 21,000 miles, this vehicle is equipped with the "Smart key system". Parked vehicle at local walmart store locked doors with push button at exterior door handle, I had left the key fob in the vehicle! ! the doors should not lock in this situation, however they did! after shopping I returned to vehicle and tried several times to unlock doors, the doors did not unlock. Had to have friend drive me home to pick up spare fob. The spare fob unlocked the doors. Notified Toyota dealer (nourse, chillicothe ohio) who advised me to go to local radio shack and purchase a new battery for the fob. I purchased and installed new battery and the fob begin to work again. I did not receive any warning that the battery needed changed! I could have been many miles from home when this happened, scary thought. I must say this is the only trouble I've had with is vehicle.