Allpowers Solar via Amazon offers Prime members the Allpowers 20,000mAh Dual USB External Battery Pack for $13.99 with free shipping. (Non-members can spend $35 or more to bag free shipping; otherwise, it adds $5.99.) That's a buck under the lowest total price we could find for a similar item and the best price we've seen for a 20,000mAh battery pack. It features a 1A port, 2A port, and an LED battery indicator.