Two problems related to battery dead have been reported for the 2002 BMW X5. The most recently reported issues are listed below.
Was driving home and my dash lights started to flash on and off after I shut the car off my and pulled the keys out my left rear tail light stayed on the next morning my battery was dead. So I pulled the battery and charged it now when I connect the battery all my lights flash randomly with no key in it. I have not driven the car for 3 months it is not safe and the nearest BMW servies is 40 miles away . I have a recall for the air bag , but not taking a chance on driving it to get fixed.
Heat/ac kept blowing after car was turned off causing battery to die so the car wont start in the morning. Original part was defective BMW knew about it and upgraded the part. Which I bought on ebay then the problem was solved. The name of the part that is defective is the final stage resistor. BMW will not issue a recall for this problem.