Up first is the Aigo aiPower i616 which alleges to provide “virtually double” the battery life with its 1,500 mAh battery tucked inside of it. Not only does it look to offer ample protection, but it adds the convenience of a hidden USB ribbon cable which instantly allows you to charge and sync your iPhone 4. Additionally, there is a microUSB port built into the left side of the case to enable you to use a longer cable if the ribbon one isn't ample enough. Finally, there is a physical button on its back that measures the current level of charge when it's pressed. If this is something that might raise your eyes, just expect to dish out $80 for the Aigo aiPower i616.
Looking a little bit relaxed and not as all encompassing as other battery cases, the InCase Snap Battery minimizes the amount of add-on luggage to your iPhone 4. Granted that it leaves some of iPhone 4's sides exposed to the elements, its soft touch exterior will still provide a bit of cushion to lessen any blows to the handset. Moreover, the snap on case is claimed to be the slimmest around with its 900 mAh battery in tow. So if you want to show off the beauty of the iPhone 4 by minimizing its overall size, then the $60 InCase Snap Battery just might be right up your alley.
source: InCase & Aigo via Engadget