In series (assuming they're 12V [please correct if I'm wrong]), then in series you'd have 36 Volts. you don't want that for a GC. In parallel, are they already 4700 MaH? If so then you'd get a just about 2 hours (give or take). If each one is 4700 MaH then you'd have 14,100 Amps (ha) giving you roughly 15 hours of playtime (someone can correct that if I'm wrong).