It's been awhile since I have posted...I often just lurk. However, I have had the same battery issues with our '09 X5d. In Dec 2010 the battery died and left my wife stranded at her work. Outside temp was about 26 degrees. In March 2011 after loading up the X5 to go to Prague, the new battery died. Outside temp was around 43 degrees. When I brought it back to the dealer they said it was the heating system near the fuel strainer that wasn't shutting off. Although this past winter was a bit cold here in Germany I am not so sure this was the issue. We'll see. I'm a bit frustrated with the ownership experience with our X5 with the two dead batteries and a few other issues in the last two years. However, my wife and I love to drive this SUV! Such a dysfunctional relationship with our vehicle. :-)