Turning off when charging sounds like a way to prevent someone to follow through with the shockingly brilliant idea of doing that while plugged in to the wall socket.
Meanwhile the Apple Mouse thing was (I presume) Johnny Ive & his obsessions getting in the way of real world usability. I don’t think anyone is going to die if they use an Apple mouse whilst it’s plugged into a usb port!
Sounds like your specific one has a defective battery. Or design.
Though, it's a not a direct replacement of Braun Series 7 mentioned in TFA - it's mainly a trimmer.
Heck, buy one even if you shave more often.
You don't have to shave down to the skin, you can use it to trim a beard. I've been doing this for years.