ThirdRail has introduced a product that addresses one of the common issues of the iPhone — no replaceable battery. The ThirdRail system contains of two elements, an iPhone 4 case and a smart battery. The ThirdRail case is a slim case with a unique feature, you can add a ThirdRail smart battery that will charge the iPhone. Need more power, then attach an additional smart battery and get double battery capacity. The smart battery works both with the iPhone 4 case (additional cases for other devices will be available later this year) or using the built-in micro USB port (it can charge multiple devices together). The system bundle cost is $90, when the smart battery cost is $60 and the iPhone case costs $40 when purchased separately.