Scosche GoBat II

The beefy GoBat offers a few performance tweaks the others can't, including the ability to charge itself and two other devices simultaneously when it's plugged into a computer. Another unique feature: its ability to play nice with Scosche's battery-monitoring Revive app, which provides a lot more information about power usage than the typical four-LED indicator system (handy data such as how long plugged-in devices need to refuel, and how much time you have left for various activities such as listening to music or turning on your phone's mobile hotspot feature). It takes a long time to charge itself, though, so expect to give it a full seven hours if you want to max it out. And you will want to max it out, because despite its big battery, it can only charge an iPhone between two and three times, and only got our iPad 2 up to 60 percent before needing to be plugged in again. [$60; scosche.com]