Best Buy via eBay offers the PNY PowerPack 2,600mAh Portable USB External Battery Pack in Black, model no. P-B-2600-1-PCV-RL, for $3.99. Choose in-store pickup to dodge the $2.99 shipping charge. That's a buck under our December mention of a different color and the best price we've seen. (It's also a current low by $10.) It features a 1-amp output for rapid charging and comes with a microUSB cable.