[Al Skierkiewicz]

There is a failure mode on the 5 volt convertor that will send 7 volts to the radio on full battery voltage and then as the battery goes down so to does the output of the convertor. It acts just a like a resistor. I believe that the failure mode is caused by a reverse electrical connection at some point. Double check the output voltage of the convertor.
Blackflame, the camera body is connected to the negative lead of the power supply. If you have other frame shorts, it is possible to shutdown the power supplies in the PD as reported by it's designer.