That is frustrating.
I would try to find another, fully charged, suitable 18650 battery somewhere to test your Terminator mod.
If the test battery works in the
device, we can presume the problem is with the on board charging circuit.
If you can source an external charger, chances are good that the battery can be revived.
You could then test the mod for proper function.
If the charging circuit is the problem, you can still use the device with an externally charged battery.
IMO, an external charger is a WIN-WIN.
Best of luck
I