Dang looks like it could be a deeper issue.
I've read about a battery cable recall for e90/e92/e82. Not sure if it would have been performed here in Australia though?
The battery positive cable that goes to the fuse box was a bit flakey on these cars. It is located behind the glovebox.
Sounds exactly like the symptoms you describe:
SIB document:
http://www.e90post.com/forums/attach...1&d=1364258411
http://www.e90post.com/forums/showthread.php?t=820077
http://www.e90post.com/forums/showthread.php?t=804545