We do tons of activities on our iPhone devices, whether it be watching a movie, listening to music, playing a game or simply attempting to type up a few notes on the miniature keyboard. The functionality of the iPhone is amazing, but there is a main flaw. What is the flaw? It's the battery.
You may be in a store, looking at your shopping list or simply playing "Angry Birds". Unfortunately, (especially with the iPhone 4S,) you will get a huge battery drain.
Here's the solution from Mophie: The Mophie Juice Pack Air.

As a short summary of the Juice Pack Air, it is a device which essentially doubles your phone's life while keeping the iPhone's ability to sync and charge. However, there are a few flaws but first, I will start with the advantages. The case charges with a 1500 mAh battery.

The Advantages
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The case itself is very aesthetically pleasing. It certainly does bring a smile to your eye. When using my white case with my white iPhone 4S, you could barely notice a colour difference between the case and the phone itself. As for the battery, it does what it says. Instead of buying a cheap case, you can go with Mophie's Juice Pack Air. While on standby mode, it has boosted me to 100% from 20% but be aware, you're probably going to get a less charge if you're using your iPhone while it is charging. Finally, the case is a two-piece case, meaning you just slide it in after lining it up in order to piece it together. Simple.

The Negatives
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There is really more or less no negative points, except for this one. You must use a micro-USB cable to connect it to a computer or USB charger. If you are using a docking system, then you have no choice but to take the case off. However, the case's design is a functionality due to its simple detachment to take it off.

Summary
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This case is a must have, seeing the excellent functionality and design. I rate this five out of five stars.

I hope you have enjoyed my review. :)