Had a similar problem Phone went to zero on a reboot and would not accept a charge was cycling. Couldn't stop the reboot cycling. All charging equipment, cords ports etc. were good. never allowed a charge although the charge sign would come on and go off as the phone cycled. The final fix was to remove the battery, I had another phone so I swapped them. This fixed the phone, I am assuming I had a software glitch causing the issue. The battery removed worked fine in the other phone. i.e. accepted a charge.
There was a change to the phone that allowed automatic app updates a few days before the issue arose.