The Gorilla Gadgets CHR-150 16,800mAh external battery pack is currently on sale for $39.99 on Woot. The site lists this as a savings of 71% ($100 off its original $139.99). This undercuts the price currently displayed on Amazon, where the battery goes for $69.99. This Woot deal, which will be over before the end of today, costs nearly half as much.
Gorilla Gadgets' external battery comes with an LED screen that shows how much of a charge the pack has remaining.