DeWalt is one of those names in tools that automatically makes me confident in its performance. When I was shopping for my first cordless drill motor, I saved my money and waited until I could afford one, because that is what I wanted. Not that there aren't other brands out there that are just as good (and in some cases, better), but it's my top choice.
It's pretty simple, really. Just click PoweriSite onto the battery where you would normally mount a tool, then plug your USB cable into it and you're all set. Which also means you are not limited to charging your phone, but can charge any device that has a USB charging cable. Or, you know... all devices everywhere, pretty much. And of course it draws a negligible charge from the battery, so no worries about killing your battery. Because I'm pretty sure your boss wouldn't understand if you couldn't work the last couple of hours of the day because you were out of charged DeWalt batteries, but you were perfectly able to play Angry Birds on your phone instead.
The disadvantage here is that PoweriSite only works with DeWalt batteries. Also, those batteries are pretty cumbersome and unwieldy to carry around just on their own. But if you, like me, use DeWalt tools already, there's really not a whole lot of losing involved here. This is supposed to be available in March (you can pre-order now), and costs just $18.00 US. I just pre-ordered mine, because in the course of writing this I convinced myself I needed one. In fact, had I known it was a Kickstarter project in the first place I would've already been a backer.
Source: Gadget Review