Just found this today, thinking of testing it out at defcon.
http://www.hypershop.com/HyperJuice-Plug-15600mAh-Stealth-p/p15-black.htm
The specs:
+ 15,600mAh lithium ion battery + 2 high power USB ports capable of charging 2 USB devices (even 2 iPads) at the same time + Built-in retractable wall plug for easy recharging + Extend iPad (1st & 2nd generation) battery life by up to 23 extra hours + Extend new iPad (3rd generation) battery life by up to 13 extra hours + Fully recharge the iPhone up to 11 times + Aluminum battery housing, available in six juice colors of pink, gold, blue, green, silver, black + Advanced high performance power management chipset by Linear Technology + Built-in short circuit, overcharging and temperature protection + Industrial medical/military grade AA battery cells + 1 year limited warranty
Intelligent Power Distribution System
HyperJuice Plug features a total of 15W power shared between 2 USB ports. Unlike other dual USB batteries that simply designates "high power" 10W USB port (for iPad/tablet charging) and "low power" 5W USB port(for iPhone/smartphone charging), HyperJuice Plug intelligently distributes and delivers the maximum power to individual devices irregardless of which USB port they are plugged to.