I just set up my voltage divider and things are working ok, except the values reported are too high.
A fresh 3S pack gives me 14.2v instead of 12.6.
To compensate, I made the following edit to the code in sensors.h. My change is in red.
if(g.battery_monitoring == 1)
battery_voltage = battery_voltage3 *.89 ; // set total battery voltage, for telemetry stream
Each input measured to ground shows 13.8K, 13.82K and 13.85K, which seems about right given the 10K+3.9K voltage divider.
Should I need to do this or have I borked something in my voltage divider?