Thank you for your reply Razor. Apart from the servo drawback there is no other issue with 11.1V battery source? From the data sheet it says max is 20V, so 11.1V should be safe to use. I am more concerned by the 3.3V output and the USB circuit, if that will work fine with a 11.1 main source. I have looked at the schematic but was in doubt.
However I must say that the Axon board is really an ideal solution I've came across so far..... not only it reduces the power circuit but also other peripherals due to tons of I/O. I am using BLDC motors so not concerened about the servo related issue.