A warning indicator in my wife's 2008 X5 last week indicated that there was a "high battery drain." The car started ok and seemed to be running fine. According to the dealership, the battery had a bad cell and needed to be replaced. The dealership informed me that I could not replace it with an aftermarket battery, b/c that would negate the warranty if the vehicle ever had electrical problems, so I had to eat the $580 for the dealership to replace the battery. I am disappointed that BMW would use a poor quality battery in there vehicles and (even though I am a loyal customer and have the X5 warrantied out the wazoo with extended warranties) they would not replace the battery for free. Has anyone else had issues with their X5 batteries?