@Jellby: Okay, that last one is a much more interesting observation

.
I double-checked, nothing *should* be caching that value (except the kernel itself, so it'd require *extremely* unlucky timing for your cat and KOReader to disagree if read at roughly the same time), and I definitely don't see it happening over here.
* Try 2020.10.1 (the initial 2020.10 release shipped with a... finicky LuaJIT build).
* Try disabling the battery stats plugin.