Having a similar issue with a tablet I've been given to repair.
Customer having troubles with it turning on and charging, even tried disconnecting and reconnecting the battery and he said that worked temporarily.
I've plugged in a battery tester on it, and the current going into the tablet through the charging port is inconsistent, meaning that the charging port is most likely damaged.
In order to fix this issue, the charging port can be replaced so that the battery can be charged properly again.