No idea. Guessing the battery can't supply sufficient or stable voltage.
Or failing electronics that deal with battery power (conversion).
You can root the device and explore sysctl, but no idea if that provides more info.
https://www.mobileread.com/forums/sh...d.php?t=325185
For laptops, one could check temperature that way, at least on BSDs. Though battery info was handled by some daemon/service, but that's all beside the point here
When checking dmesg, be sure to use the proper --levels:
https://www.mobileread.com/forums/sh...60&postcount=8