If you increase R1 will that muck up the RC in that end of the circuit ??? and change the oscillator

wonder if you could fit another resister between negative side if C1 and ground to current limit T1 if more volts were added ?

Im just thinking alot of people (and me) would look at a 2s lipo pack as they are so easy to field recharge less weight and more power so 7.4 volts
sounds a nice voltage to set it up for and try not using the voltage reg as there quite power hungry unles its switch mode

What do you think

brett