The photo shows a screwdriver with a long thin shank. The screwdriver I got from iFixit (with interchangeable bits) was not able to reach the screw at the right angle, and the sleeve on the screwdriver started damaging the battery. I had to remove the battery before I could remove this screw.

This step came in very handy when one of the little rubber mouse buttons slipped out of my trackpad. I pried up the back and slipped it right back in... Good as new!