New Trent Easypak 7000mAh Portable Triple USB Port External Battery Charger/Power Pack for Smartphones, Tablets and more (w/built-in USB cable)
This is very convenient when traveling. The size is perfect. But it really showed it's worth as it kept two busy iPhones completely charged during a 20 hour power failure and ice storm. Reminder for travel: take the connecting cord between this device and the one you want to charge.