From this thread, it seems like you already know all there is to know. Still, here is my summary for any newcomers dropping in:
For unknown reasons, F(x)tec ship their phones configured in a way that allows battery charging only with a running OS. If, by whatever circumstances, the battery charge ever drops to zero in that configuration, re-charging will no longer work, as this would require to first boot the OS which - in turn - would need at least some residual charge to be left in the battery. In that situation, the only way to re-charge is probably to disconnect the battery from the c