AlienPower is definitely a solid external battery for those who demand more from their devices.
I'm currently using an iPhone 5S as my daily driver and this external battery is capable of re-charging my device several times through out the week. At first I bought a 3200mah battery back thinking that smaller is always better but to my surprise something in the mid-range was vastly superior.
Now, I simply charge the battery pack once a week and simply use it when I need more juice.
Anyways, here's my video review of the product. Enjoy!