sometimes, you don't know how to choose battery fo your heli, maybe this is a simple lists for you.
Gens ace 800mah 3S for Trex 250
3S 2200mah for CopterX 450
Gens ace 3S 2200mah for Trex450 Sport
Gens ace6S 5000mah Trex600ESP
Gens ace 2600mah 6S Gaui 550
Gens ace 2600mah 6S Goblin 380