The M8 & M11 use entirely different battery holders... the M8 holders comes out and slides in.. whereas the M11/Mx-3 pretty much stays in the controller..
I just looked up the Airtronics part on
www.hobbypeople.net
Looks like they are not selling them anymore.. and Hobby People is Airtronics' importer... sooo.... ut oh...
http://www.hobbypeople.net/gallery/475048.asp
I'm glad I got a spare! I had 3 and gave one away a few months ago...
Jerome
