Hi @jojorep ,
It may be a faulty battery (even rechargeable batteries have a lifespan) or perhaps a faulty or loose micro USB charge port.
Use a magnifying glass and a strong light to visually inspect the charge port for any obstructions that may be preventing a good electrical connection. If there is anything in there, do not use a metal pin to try and clear it. Use a vacuum cleaner instead, to try and clear it.
If the charge port appears to be OK, here’s the maintenance and service guide for the tablet.
Opening the tablet will allow you to check if the micro USB charge port is securely connected to the systemboard.
If it appears to be OK then go to p.16 to view the necessary pre-requisite steps and then the procedure to remove / replace the battery.
At the top of p.16 you’ll find the battery spare part number (784326-001). If you search online using the part number only you’ll get results for suppliers, although the few that I checked didn’t show a price for the battery.