I bought the Garmin style mount and the corresponding battery cover at the same time. They fit fine.
The only niggle I have is that when the switch cable is plugged in, it sticks down slightly lower than the base of the mounting plate. This wont be an issue when mounted on a handlebar or similar. However mine is mounted on the exterior bodywork of my Dutch 'Quest' Velomobile. (Google it if not sure!). I previously mounted it on the inside, but I don't think it was loud enough, so I wanted to mount outside. I hoped to mount the Garmin-style mount straight onto the bodywork, but for now I have to pack underneath with washers to give clearance for the jack plug of the switch cable, until I laser cut some 3mm acrylic in a matching profile to the base....
