Hopefully the dealer would have the battery replaced under warranty for you. I just want to add another data point regarding the power draw of the retractable top mechanism. The car and the battery are 6-month-old, so presumably in good condition.
Every time I operate the top 3 or 4 cycles in succession without driving the car, it would show an "Increased battery discharge!" warning on the iDrive screen upon start up with the yellow car-on-a-lift service warning in the instrument cluster. So the top is obviously drawing a lot of power from the battery during operation and the battery doesn't like it at all. The car never failed to start or cranked for a long time, and after driving the car for 15 minutes, the warning message no longer returns when the car is started.
I don't have a good solution, but it seems like this is what it boils down to. The top mechanism draws a lot of power. Someone with a Bentley manual should confirm this, but I suspect the battery capacity for E93s is the same as the other E9x models, and it isn't really big enough for operating the top again and again without the car being driven, especially as the battery ages. A trickle charger hooked up while operating the top while detailing might help, but in final analysis E93 owners would have to accept shorter battery life compared to other E9x.
"Unfavourable driving pattern" is bollocks. If BMW can't make a car that has to be driven more than 5 miles a day to stay charged, perhaps we should all stop buying BMWs altogether. If the service advisor insists this is the cause of battery failure and refuses warranty coverage, I would demand documentation issued by BMW NA or BMW AG specifying minimum driving criteria for battery replacement under warranty. I doubt such a document exists (for it would be absurd), but if it does, it would make a comical read.