Aukey Direct via Amazon offers its Aukey 20,000mAh Dual-USB Portable Battery Pack in Black for $29.99. Coupon code "8XR76RMA" knocks that to $17.09. With free shipping, that's the lowest price we could find by $15. It features Lightning and micro-USB inputs, two USB charging ports, AiPower smart charging, and a built-in LED flashlight.