@dickedata , Richard , Look in the charge port and blow/pick out(carefully) any dust/debri that may be causing an issue also look in the port for any bent pins and straighten very carefully with a tooth pick. Try a different compatible charger/cord to see if that is the issue one more time. If different compatible charger/cord does not fix and port looks/test good, the battery or connection could be bad, if able to clean battery connections and reconnect/install battery, still not charging battery probably faulty. If port is found to be bad/loose/damaged , this is really not a repair for the inexperienced because the charge port for your device is soldered to the mother board and the heat generated could cause further damage if not very careful. I will post a link to a tear down guide to get you inside the Nook to check the charge port and will also post a link showing what is involved in repairing a mini USB attached to the board. you can google search for new charge port if needed. If not wanting to do the repair yourself have a good computer/cell phone repair shop have a look and estimate repair. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
Nook Color Motherboard Replacement