I have a 1600mah NIMH battery in mine, from RadicalRC.com. I can fly all day on a charge, actually two days without recharging.

Radios have some kind of witchcraft circuitry built in between the charge jack and the battery, and the battery is reversed polarity from other brands and batteries. I'm not sure but this might make charging and discharging a lipo much more of a chore than a simple NIMH replacement with which you could use your regular fast charger.

Just my personal thoughts. I hope you find something that works for you.