Canon 5D Mark II battery door

thingiverse

This is the basic shape of the battery door on a Canon 5D Mark II. It's purposefully made to be a tight fit so that you can file/sand down the edges to make it fit tightly so it doesn't pop off. It's an emergency measure until you can get a replacement door, but feel free to remix it with a latch and some sort of hinge if you like. The key component on the battery door is the small protrusion at an angle in one of the corners, which switches the camera on when in place. Without it, the camera doesn't turn on, hence this emergency thing.