If you updated to iOS 6 on your iPhone 4S or iPhone 4 and despite all our battery life tips, still aren't getting enough power to get you through the day, or if you simply travel and need to recharge on the go, the PowerSkin Battery Case for iPhone is worth a look. Like other battery cases, the PowerSkin fits snugly over your iPhone 4 or iPhone 4S -- sorry, no iPhone 5 version available yet! -- and hooks into the Dock connector to supply power.
Unlike some competing cases, the PowerSkin isn't made out of hard plastic. It's soft and silicone, which means instead of you having to take it apart to put it on your iPhone, it's a single piece and you just slip your iPhone inside. The materials used for the PowerSkin also have some other advantages. First, they're light. The PowerSkin is lighter than a lot of other battery cases I've tried (though admittedly not sleeker). Second, the materials provide for a soft-touch finish, making it less likely you'll drop it to begin with. Third and most importantly, they're shock absorbing. So, it helps prevent you from dropping your iPhone, and when it can't prevent it, it helps your iPhone survive it. Double bonus. If you're going to have to deal with the extra bulk of a battery case, you might as well enjoy the benefits of some extra impact protection as well.
The PowerSkin Battery Case for iPhone 4S and iPhone 4 charges over USB and it'll charge your iPhone before topping itself up, meaning you'll have a fully charged iPhone and a fully charged PowerSkin at the end of the cycle. You can even sync with iTunes over the cable, if you haven't gone PC Free yet.
The battery inside the PowerSkin is 1500mAh which is roughly analogous to the one inside the iPhone, so you should get double the battery life overall. The PowerSkin has a battery level indicator that consists of 4 lights and shows you the remaining charge level -- 100%, 75%, 50%, 25%, or nothing. PowerSkin rates it as providing 5 extra hours of talk time and 200 extra hours of standby time.
The design is nice and the Matte Titanium PowerSkin model I was sent to review reminded me of the look of the original iPhone -- a metal back with a black swatch, albeit across the top instead of the bottom. My only nitpick is that the inside bottom of the PowerSkin doesn't join up flush with the bottom of the iPhone, leaving a gap, so dirt can get in. I'd prefer a closed design there.
All your iPhone buttons remain accessible when inside the PowerSkin Battery Case. There's a deep cutout for the ring/silence switch and volume buttons, but it's not too hard to get into. The on/off button is covered, however, and uses a pass-through which required quite a bit of pressure to successfully toggle. You might need to do some extra pushups first. The camera, likewise, is well cut out.
If you're rocking an iPhone 4S or an iPhone 4 and you absolutely need to make it through the day and then some, the PowerSkin Charge case is a solid choice. If you want something slimmer or sleeker, you'll need to look at other options, but if you don't mind the bulk offset by the lightness, soft-touch, and shock absorbing properties of the silicone, give the PowerSkin a look.