This is the MiLi Powerskin that claims to be the world thinnest iPhone battery case. It is actually a similar product the Mophie’s juice pack air and packs the same 1200mAh Li-poly battery.
The MiLi Powerskin offers up to 19 hours of audio play time, 5.4 hours of video playing time, 3.9 hours of talk time and up to 230 hours of standby time. Other than offering additional power, the hard shell Powerskin also protects your iPhone. It works with both iPhone 3G and 3GS and is available in various colors.