Tablet battery does not charge through the keyboard

Each battery works fine on its own though, and I can charge the tablet by itself if I plug the charger directly into it. I've tried all of the software fixes on the internet to no avail. (reinstalling windows, messing with drivers, etc) I've also charged the tablet battery to 100% with no luck. I don't really see how this could be a hardware issue, but I guess it is. I thought the keyboard would've just passed though power to the tablet to charge but maybe not?

Any ideas?

Thank you