The lithi-poly batts are great. 2 cells = 7.4 volts and plenty of punch. But you're looking at $40 for a 2 cell. GP now makes cells to fit micro sized chassis. I would imagine these are good since they're made by GP. Also, if you're on a budget the Kan 1050's are good. You can buy loose cells or pack for pretty cheap at
www.blindbatts.com