Meritline offers the Dual-USB Output 5,000mAh Rechargeable External Battery for $23.99. With free shipping, that's the lowest total price we could find for such a battery by $6. It functions as an emergency backup power source for cell phones, tablets, and other devices. It includes adapters for Sony Ericsson, Apple, Nokia, Motorola, LG, Samsung, HTC, and more.

Expect this item to take two to three weeks to arrive.