Third Rail Mobility has announced the Third Rail System, a protective case for the iPhone 4 with an optional slide-on battery.

It offers add-on battery power for your iPhone 4 when you need it and doubles as an external battery solution. The outcome is a complete power solution that replaces bulky power cases, external chargers and traditional protective cases, says Brian Lemelman, CEO of Third Rail Mobility.

The Third Rail System is comprised of the world’s thinnest power-ready protective case (Slim Case) and a universal, interchangeable, removable battery (Smart Battery), he adds. Lemelman says it’s the first to provide several different usage modes in one simple system — functioning as a protective case, a power case, a portable external charger and a power hub for charging multiple devices at one time.

The Slim Case is compatible with all iPhone 4 models. Unlike cases with built-in batteries, the Smart Battery slides onto the Slim Case for a charge and can be removed when power isn’t needed.

The Smart Battery is a slim, 1.4-ounce rechargeable 1250 mAh lithium­ion battery that slides onto any Third Rail Slim Case. Through its micro-USB port, it can function as a stand-alone, universal charger for most other devices

Available at, selected retailers and online stores, the Third Rail System retails for US$89.99 while individual components are sold separately: $39.99 for the iPhone 4 Slim Case and $59.99 for an additional Smart Battery. For more information on the Third Rail System, go to .