Optimal power switching circuitry for use in a closed system such as a TET system including an internal device separated from an external device by a boundary. The internal and external devices being powered by separate power sources. During telemetric communication from the external device to the internal device an external RF energy source is produced. If the power supplied by the external RF energy source produced during communication from the external device to the internal device exceeds that required for powering of the internal device, then the power switching circuitry cuts off power to the internal power source and instead draws power from the external RF energy source thereby conserving power consumed from the internal power source. The power switching circuitry may be implemented using either passive components (e.g., diodes) or active components (e.g., an analog switch).