The MiLi Power Spring Battery Case, is nifty little iPhone 4 battery charger case. By little, we mean little, it measures a mere 18mm at its thickest point.
Of similar types of products, this is definitely one of the thinnest.
When you place your iPhone 4 in the MiLi case you notice just how bulky all your other cases are in comparison.
The case is comes in two parts which clip together. You slide your iPhone into the case and then put the top part on, easy breezy.
The case is made from a hard shell plastic, and it features a sleek black paint finish, similar to the back of the iPhone.
There is a mini 5 pin port on the bottom of the case for charging the case via USB. There is an on/off button, and a battery indicator with LEDs to show you how much charge is left.
The downside is that this like other cases has the unfortunate tendency to make the iPhone 4 look like an iPhone 3GS. It's a neat little case but ruins the profile a smudge.