Here’s a little video of an Apple G5431 mouse made wireless. It’s only one button, but still pretty cool. https://youtu.be/Nioyj4QXn_g
Also, I just watched a neat video from NFM, one of my favorite YouTube channels in Japan. It’s a quick walk through of a higher capacity rechargeable battery for his MX Master wireless mouse. Since you’re here I thought you might like this kind of thing too. https://youtu.be/s_Na4EzeWPA