The screw is tiny and is a TORX head. With my thick, clumsy fingers I managed to drop it in a crack in the driveway. It must be made of a non magnetic alloy, I could not find it with my magnet. But the two halves of the case snap together nice and tight anyway plus when you bolt it to the shrader valve through the wheel I don't see how it could come apart. I was so impatient to take a test ride I did not want to wait for a new screw. I was looking at the pictorial over at the "other site" and following along. The battery I used had different tabs, 180 degrees apart but they worked fine. They are easy to bend and flexible which makes them easy to work with. Test fit the battery before you solder it in.
As in the pictorial I held the circuit board leads with a mini-vice grip held in a vice. The battery tabs had little holes on the end. I put a bit of solder in these first, then held the tab to the lead, which already had some solder and applied heat. A couple seconds was all it took. The vice grips act as a heat sink to protect the circuit board. Once solder together the battery and circuit board both snapped snugly into the case.