You could check if you have a defective charger board like on my Pocket Reform (MNT Pocket Reform doesn't boot). If that the case and you just received yours you can send it for RMA (I’m still waiting for a new one) and use the Pocket Reform without battery.
TL;DR: access the battery compartment and see if the main IC (U1) of the charger board is super hot (check with a thermal camera of thermometer as it could be 125+°C so very hot to the touch). If yes it might be defective.