Few things are as handy as an iPhone battery case—binder clips, Swiss Army knives, and the iPhone itself. But most iPhone battery cases add bulk, and don’t always have juice when you need it most. Third Rail takes a novel approach by keeping the case and battery separate. Your iPhone stays in a sleek, attractive Slim Case that adds practically no bulk at all, just a centimeter or so at the bottom. Flip it over and you’ll see a contact strip of three gold rails—that’s where you’ll snap on the 1.4-ounce, 1250mAh Smart Battery. Micro-USB in and out ports let you charge the battery from a computer or USB power adapter and juice up other gadgets that charge via USB. If you want extra power, you can buy additional Smart Batteries for $59.99 each, and when they all run dry you can stack them on the Slim Case to charge everything up at once.