To me two weeks not on a battery tender is just about normal. The car constantly looks for the key fob and a few other things that runs the battery down. Good luck on your search i would check it in the dark to make sure no interior lights or the trunk light is not staying on. At 150 an hour at the dealer for them to look around its going to cost a good bit. I would start by seeing if your battery has a full charge and the alternator is doing its job to keep it topped off. you cannot skimp on a battery on these cars. Not saying you did but it needs a top of the line battery