Third Rail iPhone 4 Casing With Detachable Battery

Typically speaking when you hear about an iPhone 4 casing that provides extended battery life, the image of a huge, heavy and bulky casing pops into mind. The Third Rail casing on the other hand does quite the opposite.

It features a slot on the back allows the connection of a 1,250mAh lithium-ion “Smart Battery,” which can be removed as needed for charging, or simply to make the case lighter and thinner.

This is rather handy as it does not require you to have two casings – one for the extra battery and one for the time when you don’t need the extra battery. A Slim Case/Smart Battery bundle for the iPhone 4 costs $90. Separately, the case is $40, while the battery is $60. Third Rail is promising to support more electronics in the future.