Hisgadget Inc. via Amazon offers its Prime members the Intocircuit Power Castle 11,200mAh Dual USB External Battery Pack and Charger for $29.99 with free shipping. That's $30 off and the lowest price we've seen. (Non-members can spend $35 or more to qualify for free shipping; otherwise, shipping starts at around $5.55.) It's compatible with iOS devices and most smartphones and it functions as an external battery and USB charger.