https://www.amazon.com/Polanfo-External-Battery-Smartphone-Tablets/dp/B01DM713HQ/ref=sr_1_4?s=wireless&ie=UTF8&qid=1468018143&sr=1-4&keywords=power+bank+20000mah
12.51 shipped
https://www.amazon.com/20000mAh-External-Battery-Samsung-BlakBerry/dp/B00VHDM8KE/ref=sr_1_4?s=wireless&ie=UTF8&qid=1468018291&sr=1-4&keywords=power+bank+20000mah&refinements=p_36%3A-1600
10$
https://www.amazon.com/Generic-20000mAh-Power-Digital-Devices/dp/B00JQ98Q7A/ref=sr_1_12?s=wireless&ie=UTF8&qid=1468018291&sr=1-12&keywords=power+bank+20000mah&refinements=p_36%3A-1600
Plenty more at better prices.