I fly mine with a 2 cell LiPo, what's that 7.4 volts? This would equate to a six cell Nimh. Go with 1000ma up and you should be fine. The airplane isn't sensitive to battery weight, just make sure it balances. It will fly easily at half throttle.

The airplane is sensitive to wind so make sure you fly it on a very calm day. It it a real fun plane but is sensitive to airspeed in that the faster it flys the more lift it gets (highly undercambered wing) so you need to be ready to crank in a little down trim to keep it level.

Highly recommend it.