New Trent Easypak 7000mAh Portable Triple USB Port External Battery Charger/Power Pack for Smartphones, Tablets and more (w/built-in USB cable)
When travelling, I generally have a bag full of electronics, including an iPhone, iPad, Kindle Fire, Novatel MiFi, and Jawbone Jambox, all of which require USB power, and a few of which are generally needing charged.  I've purchased several batteries over the years, and I've always been happy with the New Trent batteries.  This one is no exception. With dual USB ports and 7000 mAh capacity, this thing can simultaneously bring an iPhone and iPad back to life with ease, as well as keep a MiFi up and running a