Keyboard and mouse battery-% often at 0%.

I bought a macmini M2 a few months ago. I noticed that quite often the battery-% of the keyboard and/or the mouse is at 0%. Even after changing the batteries. A few hours later it does give the right %. Sometimes it’s the keyboard, other times the mouse, sometimes both. OS is updated, that didn’t help either. I use an Apple keyboard and mouse from 2017, they worked fine with the iMac I had until I got the mini. Anyone knows what’s going on?