hello Ethan,
I don't know why most people think that if a device stops working the battery is always to blame. It's a myth. It doesn't work with battery connected but without it seems okay. Just this bootloop. The device does not start in user mode without the battery electronics connected, which is normal. You must make sure that the connection is correct and the induced current has a correct value. It's best to take the watch apart on the table and check each module. Screen works - the first step done.