This is amazing, it completely solves the battery life issue on my 4S. I was getting about a day's battery life previously, now it's 3 days. Not only does it intelligently release power to the phone, it really protects the phone, is very nice to hold in the hand, and looks great (at least the black version does). Even better, it adds virtually no weight to the phone, it's really light. It fits the phone perfectly, and is very solidly attached. As negatives, it's quite awkward to access the volume buttons on the side of the phone. Also, it doesn't come with a wall plug, just a USB charger, so you'll need a compatible wall socket plug to charge it from the electricity mains, otherwise you'll need to charge it on a USB port (which takes far longer to charge). So, why 4 stars? Really it's because of the price, it's really expensive for what is essentially an iPhone cover with a battery in it.