that's still twice what you should be paying:
http://www.xoutpost.com/bmw-sav-foru...ement-diy.html (get your own battery and bring it to an indy).
BTW, I knew my battery was dying when it started shutting off my radio (after ignition off) only after something like 5 minutes. It should go at least 15-20 minutes under normal conditions. Also I recall there was an indicator on the dash that is different from the keyfob battery low (comfort access). Since everything is dependent on the car battery, your mileage certainly will vary on warning signs.