One of the major problems I had with my iPhone 3G and 3GS was battery life, and I always ended up using one of those battery extender cases for both models. The new iPhone 4 comes with an improved battery life, much better than the previous models.
If you are a heavy users of your iPhone 4, then you may need to use an external battery case with it, one of the first ones to hit the market is the new MiLi PowerSpring4 battery case for the iPhone 4.
The MiLi PowerSpring4 features a 1600mAh battery that is designed to significantly increase your iPhone 4’s battery life. It takes about four hours to charge from empty, and once charged you will get about 360 hours extra standby time.
Talk time comes in at an extra 6 hours over 3G and around 13.3 hours over 2G, browsing will give you an extra 6 hours over 3G and over 10 hours on WiFi. Music and video wise, the PowerSpring4 will give you an extra 36 hours of music playback and up to 10.6 hours of video playback.
We have been testing the PowerSpring4 out over the last week, and it seems to perform very well. The battery life on the iPhone 4 is pretty good on its own, but if you add the MiLi PowerSring4 to it you will only have to recharge your iPhone 4 a couple of times a weeks as opposed to every other day.
The case does add a fair bit of bulk to the slim design of the iPhone 4, although not any more than any of the other cases available. It can be recharged via USB and features a microUSB port and comes with a cable so you can charge it from your Mac or PC.
You can find out more details about the MiLi PowerSpring4 over ayt CaseAddict, it is now available for £54.99 about $84.