I wanted to use my BF-F8 for a fox hunt, so I needed to attach an Arduino and power it. The backpack slides onto the grooves in the back of the battery meant to align the battery with the charger. There are 3 contacts on the back of the battery used for charging. They expose the full battery voltage (2 cell lithium) so I'm using that to power the Arduino.
As a future improvement, I'm mounting a GPS (ublox neo 6m) it the backpack as well. Initially the fox is going to be able to it's callsign and GPS position out with morse code. Later, I want my radio to transmit APRS info. I've always wanted to have APRS in my car.