It’s literally just the same body as the OG Magic Mouse, which had a bay for a pair of AAs underneath. All they did was remove the bay, put a rechargeable battery in there, and a socket to charge it. It takes a couple of minutes to give it 9 hours of juice.
There’s no grand conspiracy.
You know this thing is tiny, right? It’ll be shockingly easy to pick up and press the button. Even with cables hanging out of it.
I use a 2014 mini with all cables hanging out the back, and it’s really easy to pick up.