The IMP52D, iTorch external battery is a nice option from NewTrent for backup battery for your smartphone. I personally have an iPhone 4S and my wife as an iPhone 4. It will also charge tablets as well (only at 1A so its can seem to take a little while to do so). Since the capacity is 5200mAh, it won't fully charge an iPad 4th generation but it does come in handy when you need a least 2 or more charges on your phone. The device is compact and is smaller than most smartphones (it is thicker but width and length are smaller) and is easy to carry around with you. The capacity would be enough to get your through some heavy phone usage on a long flight or a few days of camping if the phone was used sparingly.