I woke up this morning to a totally discharged phone, though it was on the charge. Obviously my HTC One problem isn’t lint.
I went online and looked for a solution. I tried a battery recalibration, though I’m not sure what that is or what it does!
The phone is taking a charge now, but how long?
I’ve initiated a backup. If (when?) it stops charging again I’ll be in a better position to seamlessly swap phones.