Apple Watch overheating yet not charging

Running the battery completely empty could also have damaged your battery.

If you are using the original USB charging cable and power adapter from Apple, and it still does not charge, it has to be serviced.

If your Apple Watch won't charge or it won't turn on - Apple Support

this could be caused by a third party power brick, some of them dont have the chip inside of them that regulates power flow for specific devices.