Where does this tiny screw go in my key fob and where to get batteries?

Any store that sells button cells. That used to be Radio Shack. Now it might be Batteries Plus (or whatever their new name is). There's always Amazon. No idea about the tiny screw. I can't think of how or why a screw would fall out. There is only opening the shell and replacing the battery. No screws to loosen or tighten when a battery is replaced. Also, no tools necessary either. The physical end of the removable key serves to pry open the shell. There is a snap apart point in the case that it fits in and you just twist it.

 

Yeah, I don't see any screws in mine, or anywhere for a screw to go. It's possible they used different fobs at different times during production though, mine is made by Tokai Rika.

 

maybe in the circuitboard? open your other fob and maybe you will see it.
i get batteries from drugstores like cvs, walgreen and etc.

 

I just did both my 2014 PIP and 2015 Rav, no screws to be found. Batteries came from Amazon. And if course, they were different, so I have some extra 1632's ...

 

That little screw goes into the spring where the button for releasing the steel screw is located. Don't push on the release button when you have the fob open or you may lose screw and spring. You don't need it for the fob to function electronically, but it seems to put pressure on the steel key to hold it in the fob.