The iPhone 4 usually does a great job of lasting all day before the battery runs out, but on those days when you are out of the office and using your iPhone the most, you may find your battery running low in the afternoon, which means it is time to use a battery to recharge the iPhone. I've long been a fan of the RichardSolo batteries because they are tiny enough to carry around, but the downside is that they hang off the iPhone when attached — not a problem if you are at a desk, but awkward if you are on the go. The solution is to use an iPhone case that doubles as a battery. XPAL Power recently sent me a free review unit of its $70 PowerSkin case and battery for the iPhone. It works very well.
It is very quick and easy to insert an iPhone 4 into a PowerSkin. Just slide the iPhone into the connector at the bottom of the unit and then fit the silicone rubber around the iPhone. If you look at a picture of the book of the PowerSkin, there is a line near the top that makes it appear as if there are two parts, but this is a one-piece design so you don't have to worry about it coming apart.
The PowerSkin covers the iPhone's Sleep/Wake and volume buttons with rubber buttons so that you can still access those controls. The PowerSkin has openings for the headphone port, the mute switch and for the camera and flash.
The PowerSkin obviously adds to the weight and size of your iPhone. The PowerSkin weighs 2.88 ounces (the iPhone 4 alone weighs about 4.8 ounces) so it adds about 50% to your iPhone's weight. It also doubles the thickness of your iPhone; without a case the iPhone 4 is 0.37 inches, and when in the PowerSkin it is 0.77 inches. With that extra size and weight, however, you do get some protection for your iPhone. The silicone rubber provides impact-protection for the back and sides of the iPhone, and the non-slip surface makes it much less likely that the iPhone will slip out of your hands.
Once connected, your iPhone starts charging. This is a 2000 mAh battery so it roughly doubles the iPhone's power; if you are close to 0% power left, the PowerSkin will charge you almost all of the way back to 100%. There is a single button at the bottom of the PowerSkin that performs two functions. Tap it once to see between one and four LED battery status lights illuminate to tell you how much power you have left. If the PowerSkin has a full charge, you get four lights; when less power remains, you see fewer lights. Second, you can hold down the button for two seconds to turn the PowerSkin on or off.
The PowerSkin comes with a charging cable that has a Micro USB plug on one end that connects to the side of the PowerSkin and a USB plug on the other end. You can plug that into a USB port on your computer to charge the PowerSkin and the iPhone. (It will first charge your iPhone, and then charge the PowerSkin.) Or you can plug the cord into a standard USB power adapter, such as the one that comes with the iPhone, to charge your iPhone and the PowerSkin. If you connect the cord to your computer, you can even sync your iPhone while it is in the PowerSkin.
If you are looking for an iPhone battery that fits around the iPhone, making it easy to carry and providing some protection for the iPhone, the PowerSkin is a great product.