Interesting, I didn't realize that Frsky made a powerbox such as the RB-20. I have the FS40, which I tried to use in a gas engine setup, but the current flows were too low for it to read values realiably. It does work great for my electric airplanes. Based on the RB-20 manual, setup should be pretty straight forward. Go here, for a basic review of how to enable the one I have. The RB-20 should be very similar,
Current mAh Consumption ? RCdiy
Also read through RCDIY's overview of the various telemetry options, and how to implement:
Telemetry ? RCdiy
Between those and the info in the install manual for the RB-20, you should be on your way.
I see there is a thread about it on the "other" forum, which may be of help to you also:
https://www.rcgroups.com/forums/show...hlight=RB%2020