Originally Posted by WagnerX5

If you use the search engine on the site you would find a million battery issues. This is a VERY common issue with BMW's because of the amount of electronics running when the car is off. If the car sat for a month, that could drain the battery. Though they usually don't go as new as yours, it hasn't not happened.

BMW will cover everything if your X is still under warranty. It is not your alternator (since you didn't post the year/model of your X is is hard to tell if a warranty covers it or not).