My battery finally started giving up after 3 years of ownership, 14K miles, driven almost daily. For some reason I didn't think to search the forums or even RTFM, I just assumed it was some proprietary battery that my dealer would have to replace under warranty, especially since it lasted 3 full years. I felt pretty foolish when all my SA did was pop off the cover and slide a fresh CR2032 in. Probably cost me more in gas to drive over there than the battery would have by itself.
So have no fear, just replace it yourself! Cheers.
-phil | 2009 E92 M3 - AW/black/CF - 6MT and a silly grin every time i drive...