Is there a formula that will tell me how long I can run with said milliamp hour RX battery. I have a Thunder Power 1350mah 2s Lipo 20C Continuous/ 40C Burst 27A/45A.

the servos are going to have a lot to do with your run time on a battery. i would say your prob 30-45 min.

I run the losi rx packs (2000mah) and they last all day, 3 quil, and a 15 min main, so thats 33 minutes runtime with alittle practice in
between heats, so about 45min total for a 2000mah rx pack.