$19 w/ coupon + free shipping Poweradd Pilot X3 10,400mAh Portable Battery Charger Poweradd Direct via Amazon offers Prime members its Poweradd Pilot X3 10,400mAh Dual-Port Portable Battery Charger for $22.99. Coupon code "NBX883SL" drops it to $18.99. With free shipping, that's the lowest total price we could find by $9.
Poweradd™ Pilot E2 12000mAh Dual USB Portable Charger External Battery Power Bank for iPhone 6 5S 5C 5 4S, iPad Mini, Samsung Galaxy S5 S4 S3 S2, Note 4 3, Nexus 5 7, HTC One M8, LG G3, Other Smartphones and Tablets - Black
EasyAcc® 10000mAh Brilliant Ultra Slim Dual USB (2.1A / 1.5A Output) Portable Power Bank External Battery Charger. Use this external battery charger so you don't need to worry about being disconnected in case you run out of battery. $50 retail price, $25 sale price.