It's a seeming inconvenience, to be sure. But in my case, I had a prefectly functioning Magic Mouse 1. When I decided to upgrade to Magic Mouse 2, I simply turned off the MM 1 and placed it into the box that the MM 2 came in. I've a battery watch-dog app that places the battery charge level in my screen-top menu bar - displays a percentage of battery life left for the MM2, and if I click on it, I get a percentage level for my Magic Trackpad 1.
So, if the MM2 drops too low, I place it on the USB cord and then I either use the trackpad or get the MM1 from is box and use that while the MM2 is charging.
Not a big problem.
But I am trying to get into the habit of plugging in the MM2 each night as I go to bed.