For a little 30 bucks, 7.4V 5200 mAh 30C LiPo: http://www.dealextreme.com/details.dx/sku.51196
What's even greater: Those will discharge at ~ 1.3 Ah or 0.25C, while they charge at approx. 0.75 - 1 C, meaning they charge up to 4x faster than they discharge (~ 1 hour)