Naphos via offers the New Trent iGeek Dual-USB Output 9,900mAh Rechargeable External Battery in Black, model no. IMP99D, for $39.95 with free shipping. That’s the lowest total price we could find by $25. 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.