That is an early video with some screen shots that may not reflect the finished product. The TX in the video does not even appear to be on since the LED is not illuminated.

I am not aware of any voltage connection that uses the S.Bus2 port. Voltage for the RX is read from the receiver bus itself. Voltage for an external battery connects to the small plug on the end of the RX opposite the servo plugs. That connection can read a second RX pack, or the RX pack before the regulator.