Interesting thread guys.
I have a 2011 E93 328i. I too had this problem. Battery was just shy of two years old and I was getting this message: "Increased battery discharge" on my iDrive screen.
The dealer replaced the battery for me under warranty after saying the battery was "toast."
I think these cars have a ton of electronics that are running and drain the batteries quicker than most other cars. Either that or the short trips are killing it. By the way, I'm not using the remote to put the top up/down any more but rather doing it with the engine running.
Jay (in San Antonio, TX)
2011 328i hard top convertible (E93), titanium silver with black interior, bamboo anthracite trim, iDrive, Navigation, Comfort Access.