I use nothing but 300 and 350 nimh packs for 1/2A. I've heard that Berg RXs run fine off of 7.2 volt packs, but haven't tried it and don't know which servos are OK with 7.2 volts. Lighter weight lipos might make a big difference if you're into 1/2A 3D [hovering] or all out speed in a tiny air frame.