BMW Repair: Battery Drain, auto mechanics, bmw 325i

Question
Hi Don,    I have a 2003 BMW 325i.  I have not been able to get my car started three MOndays in a row.  And coincidentally, the car was not driven on the Sunday before each of the Mondays.    When I turned the key, I could hear a  click  and then nothing happened.   Each time, I would call Road Side Assistance and someone would come to give the car a jump.  Then, I was able to drive the car back to the dealership.      The dealership has finally agreed (after my third visit in 3 weeks) that something is draining the battery.  However, my car has been at the shop since last MOnday but the dealership still hasn t figured out what went wrong.    Have you encountered similar problems before?   Could you please offer some advice?    Thanks a lot.

Answer
I have not encountered this problem from cars before but have with auto mechanics that I worked with at past dealerships.Seriously now.The problem sounds as if the battery was low in charge the first time it was jumped.Although the battery is charged by the altenater,it is only enough to keep a battery with a full charge up when the vehicle is being used.So finally when you got it to the dealership it may have been charged enough to pass their tests.Have you replaced the battery?The life of a battery is maybe 5 years with proper maintenance.