Additional diagnostic information: 1. Disconnecting the USB cable from the UPS to the computer stopped the error messages (both kinds). 2. With the cable disconnected the KDE battery applet no longer showed anything. Which suggests some information, specifically the UPS model was getting through. 3. Reverting to the previous kernel, 5.10.0-44-amd64 (from `uname -a`) and reconnecting the cable also results in no errors.
Conclusion: 1. The problem is specific to the 5.10.0-45 kernel. 2. It is caused by the connection to the UPS. I have not tested if plugging the cable into a different port on the computer makes a difference. Some of the USB ports on the front of the computer do seem to have failed. The UPS and most everything else is connected to the back.
