BMW Repair: 2001 530i chronic dead battery, 7 digits, bmw dealer

Question
This is our second BMW to have seemingly undiagnosable dead battery issues.  The current car is a 530i 4 door sedan, last 7 digits of VIN are CF09354.

We have had the car for 2 years and the first winter did not have problems, but this year the battery goes dead for no apparent reason.  We put in a new battery and in less than 2 months we had another dead battery.  The dealership ran an $89.00 diagnostic on the car and said it needed a NEW BATTERY!  We had the battery in the car checked and it checked out fine.  The mechanic and NAPA were willing to replace the battery, but given my past history with BMWs I did not have this done.  My mechanic found an on-line bulletin which indicated that the 530's have a problem that when the temp. hits 40 degrees the radio comes on and drains the battery. It indicated that the radio needed to be reprogrammed, which I asked the BMW dealer to do and they indicated they performed.  A few days later I went to the garage and the car was dead.

My husband works out of town a lot and even though this is "HIS" car he is afraid to take it on jobs for fear he will come out and have a dead battery.  

This is very frustrating and frankly, since neither of us are a member of the bar association our local dealership really doesn't seem too anxious to go out of their way to assist.  They are much more anxious to sell new cars and serve their high end customers than in being of service to someone who bought their BMW used.

Since we had this exact same problem with a 325i (1983) convertible, we now have a much less high opinion of BMW.  That car had MANY new batteries in its' lifetime and we finally traded it in on the 2001.

Do you have any suggestions to cure this problem or do we have to trade it in on something else to get it out of our hair?  We like the car, and are loathe to pass the problem on to someone else.

Thank you for any assistance you may be able to offer.

Joyce

Answer
Joyce, I doesn't sound like you expressed that the battery is dieing repeated to the dealer. If the battery is sufficiently discharged it can ruin the new battery. You need to charge the battery fully and ask the dealer to perform a closed circuit current draw test to see if the car is entering sleep mode properly and how many amps it is consuming from the battery once it is in sleep mode. Chances are good that the vehicle will not act up at the dealer as you mentioned that it took 2 months for the battery to become discharged. Make sure you disconnect any and all aftermarket accessories (cell phone charger, radio/amps, radar detectors, etc.) and see if the problem persists. Two components that come to mind that can cause excessive power to be used are the A/C final stage resistor pack, and the electrical portion of the ignition switch on the left side of the key tumbler. Both of these components WILL go bad with time on your vehicle and I recommend replacing them to any person with a E39 five series car. The Ignition switch will cost about $40-$50 parts only and the resistor will cost around $100 dollars for the part. I think one of these components are causing your issue, but I would let the dealer take a CCCD reading as I mentioned before. If the new battery you have is a BMW battery you can get it warrantied if it failed in less than two years under a parts warranty. Wish you luck
-Evan