New Trent Easypak 7000mAh Portable Triple USB Port External Battery Charger/Power Pack for Smartphones, Tablets and more (w/built-in USB cable)
Haven't had the battery pack for that long, but so far it does what's supposed to do. I was able to charge my iPhone 4, 3 times before the battery pack needed to be recharged. Hopefully it can maintain that kind of charging power the more I use it. Only time will tell.