how to remove the battery cover on the wireless mouse?

While this is marked answered, the answer didn't help me.

I found that I had to use this process:

1. Hold mouse in left hand with black tab at bottom.
2. Insert right thumbnail in slot on "up" side of black tab as held; i.e., the side towards center of mouse.
3. Push in and down. This will release the cover but typically not completely. YMMV.
4. Place thumbnail on top of black tab and push down as you slide thumbnail down towards bottom of mouse. Thumbnail will catch the edge of the opening at "bottom" of black tab and pull the cover off.

Replacing the cover is only a matter of inserting the top edge and then pushing the cover down into place below the black tab.