With a good stock gun you can safely run a 7.4 LIpo. Just avoid long burst.
Here's the one I use in my Sam-r with and M120:
http://shop.ehobbyasia.com/bb-batter...miya-plug.html
And the charger:
http://shop.ehobbyasia.com/cxi-gs-10...v-battery.html
The batterie fit nicely in the crane tube and make you weapon system ligther. It's a win win