I've had a few different cell phones in my life. Sure, the first one was the big, bulky Motorola case that was more like a lunch box than a portable phone, but after that they started getting smaller and smaller, and not needing the external battery. The life of the phones were decent, requiring me to charge them about once a week or so depending on how much I use them. But then again they were only used for making calls.
With the more advanced features being implemented in smart phones, the devices are being used for much more than just as a phone. I watch movies, play games, surf the web using WiFi, check e-mail you name it chances are I'm doing it on my phone. But this also means that I have to charge it much more often, usually every night. And that is just from intermittent use throughout the day. The next time I have to travel, while I will be entertained, I don't expect my phone to have any charge left by the time I land.
That where products like the morphe juice pack air comes in handy. This is basically a hard case for the iPhone that doubles as an external battery pack. Basically you slide the iPhone into the case and, with the flick of a switch you can operate on a separate battery supply to prolong the life of the phone.
It does add a bit to the iPhone. The dimensions increase by 0.4" (height) x 0.19" (width) x 0.27" (depth). Access to all of the buttons are still available. And interestingly the USB connection has been replaced from the proprietary Apple cable to a standard micro-USB port (common on most smart phones I've been analyzing), which makes charging and downloading content a bit easier. However, other external components can not be used without removing the iPhone from the case. This can be a bit of a hassle if you want to plug your iPhone into something like an external stereo.
According to mophie, the Juice Pack Air provides an additional 270 hours of standby and 4.5 hours of talk time, or 20 hours of music, or 6 hours of video. However, what I find drains the battery the fastest is playing games. Playing a game on the iPhone can last for about 2 hours before the battery requires charging. With the Juice Pack, I can get nearly twice that amount of time before needing to recharge.
The Juice Pack does what it says it is supposed to, which is to extend the battery life of the iPhone. It also doubles as a protective case for the iPhone and, while adding a bit of size and bulk to the device, does not feel uncomfortable. However, there is no screen protection, but this can easily be added on after the fact.
