Step 1 – Undo the screw.

Using a screwdriver with a security screw bit, unscrew the screw which is located in the battery case, just above the RED DOT in the picture.

There is no screw under the label, so don’t do this:

Step 2 – Separate the case.

It hinges to the front:

Step 3 – Done.

The RED DOT in this picture shows where the mouse “buttons” are.