Third Rail System (for iPhone 4)

Pros: Thin case, thin batteries for bulk-free battery power. Smart Batteries are hot swappable, stackable and interchangeable, which means if one battery runs out, your other batteries can recharge it. It also includes cables to charge other devices, too!

Cons: The only con is that this doesn't come in more colors. I want another!

Summary: I just bought this Third Rail case on Amazon with a gift certificate and it's awesome! The Third Rail case combines protection and power: its slim, bulk-free case protects your phone in style but it also allows you to slap on a battery when you need to recharge. When attached, the battery adds some bulk but its short recharge time makes this a quick and easy recharge process. I also bought an extra battery pack so I could "stack" them (as they say on the Amazon page) and get more batt power. Let me explain this: the smart batteries consolidate the charging. The smart charging will drain the battery with the least power first, giving it to the next most charged battery. This way you won't have two half-charged batteries to carry around. It's pretty cool device and I'm super happy with this purchase.