The third rail system is equipped with a 1250mAh battery, but you do not have attached all the time. If you feel like you wear skinny jeans or just not you will do much to touch your phone, you can remove the battery from your machine to let the light and tight. Keep it in your bag and be ready when you need, just fold it and you're good to go.
A nice feature is that the batteries are exclusive to the iPhone. You can use other devices to charge from USB. This is useful if the camera happens to die at the wrong time, but you have your third rail. Indeed, the battery can be stacked four deep and loads of electronic gadgets at once!
The entire system will cost you $ 90 and you can buy additional batteries for around $ 60 a pop. Also, if you solve your case or your half, you can choose one of up to $ 40.
This system is also compatible with future iPhone cases, so you can keep the battery as you upgrade your phone.
