This is one of the most sound investments I've ever made.  A few times since I've had the power pack it has saved me from being without a phone.  It charges electronic devices (my new iPhone 5 in particular) about twice the speed of a normal charger.  It's lightweight and so small it fits into a cup holder, purse, pocket, glove box, almost anywhere you can think of.  Because it's USB  you can charge any cell phone and many other electronics.  It charges my new iPhone from empty to full 2+ times before needing its own recharge.  One of the things I really love about this is I can have it at home for whenever a need a super-fast charge or it's affordable to even have a second so I can just leave it in my glove box for an emergency.  When I bought this two of the features I didn't know it had was a laser pointer, great for teaching and a super-bright and flashlight, again great for that emergency.  The charger itself is super easy to re-charge, you can charge it via an electrical outlet and you can also charge it using your computer's USB.  Looks like I have most of my Christmas shopping done just buying a few more of these.