These tablets take around 4 hours to charge from a flat battery.
Consider getting a USB ammeter which you can find online on eBay to check the amperage output of a wall charger.
Make sure you are using a 2A wall charger and as said from the other answer another charging cable if you haven't already.
Chances are the charger port needing replacement from being worn.
Just pointing it out there but there have been some cases where liquid damage / corrosion was found behind the charging port inside the tablet.