I just wanted to remind OSD users, especially MinimOSD users, about the MAVBoard indiegogo campaign: http://www.indiegogo.com/projects/mavboard. It's just about at the half way point and is a little less than half way funded!
One of the primary uses of the board is to make connecting the MinimOSD to the ardupilot very easy when you have multiple telemetry devices.
I'm happy to answer any questions about it.
We only have the full voltage, so we try and detect cell count by total voltage, and then we return back the total voltage divided by cell count. It's not perfect but it does give a very good sense of what is going on voltage wise.
Yes, the slight difference in cell voltage is because of the rounding. Yes, we could only show an average of 1 cell, but then the FrSky LCD would show a total voltage of only the one cell count. My opinion is that it is better to have the total voltage over the telemetry, so that some telemetry systems (like the Taranis) can actually give you an audible warning of low voltage.
The basic idea behind this project is that the APM has pretty much all the telemetry you need to feed the FrSky telemetry without actually needing sensors/hubs. Merging actual sensors and mavlink data into one stream seems possible but complicated. If one were to want to do that project and provide code that runs on the mavboard, they are certainly welcome to do that! :)