I modified this model by making a double battery holder in one piece to make it easier to mount as many as possible on the wall and to make it easier to align with other holders if there are more of them.

I also removed the slight slope that the model had, which was located at the end of the battery, which was causing me problems in that when I insert the battery into the holder, it sits on that slope and rises on it, which then causes the battery to "get stuck" in the holder and more force must be used to pull it out.