I have ti nspire cx cas. It hasn't been charged in a while, so I left it plugged for all night. After that time it still was at "critical". My battery indicator cycled between states "charging" and "running on external power source". Also in menu entered by pressing
under battery charging test, under option "battery pack connected" it cycled between yes and no option. I thought that battery may be too much drained so I took it off and charged it with lipo charger. After plugging it back my calc went to bootloop. Interesting enough when I start it w/o battery it boots up normally. In menu under battery pack test there is big blue cross, text saying original voltage 4.4V and "original voltage error". Under charging test nothing changed. This is my first post, so sorry if wrong place.
