Battery Calibration - Battery Percentage Going Down While Off-But-Charging (Pixel 5a)

My phone (Pixel 5a) went from 100% battery to off quite quickly, and it had been doing so. When it died from 100%, I turned it back on. It turned on, showed 0%, and died within a minute. I plugged it in (via USB-C, not wireless). While off but charging (without interruption), I checked and found it steadily increasing toward 100%. I saw it at 93%, then 97%, but then it went to 96%, 95%, and 93%. Hours later, it's still plugged in but showing 92%. Is the battery discovering that its maximum charge is much higher than it had been? Or, despite a charging animation on the "off but charging" screen, is the phone discharging? I'm not sure about the version, but it is the latest standard/stable OS and security version as of today (2023.10.23).