[knc1]

This problem sounds familar for a K3.

If a K3:

*) Sometimes they "just quit" - - if anyone has found out why, they haven't posted it here.

*) The battery management chip is under firmware control, firmware not running correctly almost always means no battery management working.
I.E: Can't recharge the battery that is installed.

*) The very long boot times almost always means the boot-up code is trying to correct file system errors. A very slow process.
Leave it on a wall charger for a few weeks (really: weeks), you might get lucky.

*) The eMMC storage chip has a complex and power hungry sequence of operations internally.
If the battery runs down while it is "busy" it will self destruct.

*) The eMMC storage chip has a limited life time and a K3 is getting pretty old.
But there is no telling what the chip's usage pattern has been over the years, all that can be done is keep in mind that they do wear out.

You can probably find a used K3 for sale at a very low price.
Or maybe even a newer model. Try e-bay if you have e-bay in your country.