eCase via Amazon offers Prime members the Kmashi 10,000mAh MP816 External Battery Pack for $11.99 with free shipping. (Non-members can spend $35 or more to qualify for free shipping; otherwise, it costs $6.55.) That's $2 under our January mention, $38 off list, and the lowest total price we've seen. It features dual-USB ports, four status LEDs, and compatibility with most USB-driven devices.

Update: The price has increased to $13.98.