I did it on my 1 series and while I just glanced at my 6 series it looked like pretty much the same setup. I suspect all the series are basically the same.
Check out:
You just have to remove the nut at the positive side of the battery to remove that red assembly. What that is, is two fuses, a 250 amp fuse for battery power to the starter and a 100 amp fuse for the rest of the car. The 1 series is like the 6 in that the battery is in the center of trunk that makes it easier than the battery in the video. I'll check it out a little more thoroughly tomorrow.