The Casemate Extender is right about in the middle of the pack as far as our recommendations go. The version we have was made for the iPhone 3G or iPhone 3GS, so I can’t speak to whether the Extender for the iPhone 4 works better. I’m not saying that it was a waste of money, but it could have performed better.
The Casemate Extender charges via USB cord and USB cord only, which makes me automatically knock it down a few pegs. I prefer to have multiple ways to charge. That being said, it only takes about an hour to and hour and a half to fully charge this battery. Once that’s done, fitting it to your iPhone is fairly simple. It’s a snug fit, though, so make sure you line up all the grooves correctly.
After it’s on, it doesn’t begin immediately charging, which is a positive in my book. In fact, you can have your phone already in it while it charges up without it wasting battery keeping your phone alive. Because it’s a pretty sturdy case, this means that you ca use it as a protective device for your phone when your phone doesn’t need charging.
However, once that battery goes into the red, just press the button on the back of the Extender until it begins to charge the iPhone. From there, it will keep charging (even if you are actively using your phone) for about two hours, at which point it will die. However, it does give you roughly 70% battery power back before it does that, so the tradeoff is pretty good.
As far as usability goes, two hours isn’t great. The Mophie Juice Pack Air will give you more time and is also a case. However, if you’re looking for a fairly inexpensive way to keep your phone protected and charged, you won’t go wrong with the Casemate. It’s also pretty light and slim, which helps keep your phone comfortable.