BMW does something for a reason...if you turn on your radio for 60 minutes without the engine turned on your battery would likely kong and need to jump start later.
Talking from self experience...haha. Was doing something in my car, key in ignition while listening to the radio. Forgot how long I was in there..suddenly radio stops and I tried to turn it back on and......nothing. Tried to crank the engine to recharge the battery....nothing.
Continued to do the job in the car...and about half an hour later successfully done a restart....weak sounding at first though.
Learned my lesson...