Luzy's Storage Place via Amazon offers Prime members the Francois et Mimi 8,400mAh USB External Battery Pack in four colors for $12.99 with free shipping. (Non-members can spend $25 or more to qualify for free shipping; otherwise shipping adds $5.55.) That's the lowest total price we could find for a comparable battery power bank by $31. It features indicators lights and comes with several adapters suitable for most types of charging ports, including iPhone, iPad, and iPod.