Here is an awesome little Power Bar Duo from SP Gadgets for the GoPro Hero3 and Hero3+.
Charge your Go Pro Batteries
This bar allows you to charge 2 GoPro batteries and a third device all at the same time. That's right, charge 2 spare batteries as well as the one inside in your GoPro at the same time.
Need to charge your phone or tablet?
No worries, simply plug its USB cable into the USB out slot on the Power Bar Duo and away you go.
Charge through the mains or as a Power bank on the road
You can charge by plugging the Power Bar Duo into the mains, or while out on the road by using the internal power bank. - Just don't forget to charge it up when you get home so that you have some juice next time you head out.