You could go for more milliamp rating. That would definately give you more run time!! Or switch to lipo! I recommend you attach the battery with velcro only, you have to remove the stock battery holders and use a flat piece of plastic to mount sticky back velcro on it and the battery. That way when you crash the batt gets ejected instead of weighing the heli down and snapping the landing gear!! it has saved me lots of money and I have never had it fall off while flying like with my stock rubberband deal!!!
What kind of running time are you getting? I usually get about 11 minutes average with my 7 cell 750 mah nimh stock batts on the gws dragonfly.
I have 2 batts and switch them out and that is a lot of flying!!! I spray the motors down with office duster held upside down to cool my motors off real fast when I change the batts out!!!