By using this a reasonable standard battery that is intended original legally for Galaxy S3's, you can conveniently mount with many charged batteries and so always have a spare battery for the iPhone in your pocket. Also you can get over it, when a battery is defective times, because you have not disposed of the entire envelope then.
Since very wahrscheinlch the batteries for the S3 are still available as long as the iPhone 5 or 5S hold, there should be no problems even of spare parts.
The only catch to the system is that you can relatively cumbersome pushes the Iphone in the envelope and then a silver frame around the Iphone is clipping, which is solved better at other envelope manufacturers. Therefore, it is removed from the shell, for example to the iPhone in a charging cradle in the car to place, a bit difficult. But the benefits outweigh.