Best Buy offers this PNY PowerPack 2,600mAh Portable USB External Battery Pack in six styles (Zig-Zag pictured), model no. T2600, for $12.99. Choose in-store pickup to dodge the $2.99 shipping charge. with free shipping. That's the lowest total price we could find by $8. It features a 1amp output for rapid charging and comes with a micro USB cable.