M12 Milwaukee battery TAB FIX (the version that has a single screw on the bottom).  

A M3 16mm screw is used to replace the original 18mm Torx tamper proof screw.  The original screw is removed with either the appropriate security driver bit or by peeling away the surrounding plastic to expose the side of the screw from which pliers can be use to grip and turn out.  See all the photos for reference.

BOM: One M3x16mm FHCS screw