Open Kindle, test the battery (it has probably died of old age).
Replace with new battery.
Note: The above advice is next to impossible to follow on a K4.
The K4 is the one which is glued together with the battery semi-permanently stuck in-place.
Trying to remove it almost always destroys the battery and/or the device.
Our master prefix index (in the K4 section) has (**should have**) a link or links to tearing down the K4.
Check those to see what your up against.
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#6,000 and it just had to be about a dead battery.
Time to retire (again).