Amazon is carrying the Anker Astro3E 10000mAh Power Bank for $33 using code EV8R3TKE. That's $67 below retail and the lowest historical price. This is Lifehacker's most popular external battery pack and an easy recommendation at this price. The Astro3E will completely charge an iPhone 4-5 times. [Amazon] The ultra-compact Astro Mini is also on sale for its lowest price of $20.