Cellular Factory offers the Dual-USB Output 6,600mAh Rechargeable External Battery in Black for $23.49. Coupon code "XQW027" nets free shipping. That's the lowest total price we could find for a similar device by $25. (We saw a 5,000mAh external battery for $24 a month ago.) It functions as an emergency backup power source for cell phones, tablets, and other devices. It includes adapters for Sony Ericsson, Apple, Nokia, LG, Samsung, and more. Coupon ends March 14.