Nexus 5x battery problem

if it says its charging while its not plugged in, this means there is a short in the charging circuit.

this can include, battery, Charge port, or Motherboard

Start by scrubbing the port, and ajoining board area with a toothbrush soaked in99% isopropyl. its a long shot, but sometimes cleaning the board is all you need to do.

try changing the charge port, as it is the most likely failure. replacing the port usually gets this running properly.

next most common is the battery. there is a small circuit inside each battery, which is continuously exposed to heat, and can fail.

if your motherboard is failing, then you will need to replace the motherboard.