I have had this problem for a while now. When the battery gets to 50% or less my Kindle will shut down. I tried the 40 second reboot, and also got rid of my cover with magnets in it. Does anyone know how I can solve this issue?
Other than talking to Amazon, which you will note is suggested by two different Moderators, not a lot else you can do. Sounds a lot like it is dead or dying and Amazon doesn't repair things. if it's under warranty, talk to them, if not, consider a new one.
Sometimes devices will get a mind of their own and/or "get an attitude" for a bit, then go back to normal. Sort of like a child throwing a temper tantrum. Keep giving the reboot a try, as sometimes it takes two or three of those to clear up a big glitch (hold the button for 30-40 TIMED OUT seconds, and it needs to be unplugged). If worse comes to worse, there's the dreaded Factory Default Reset.