I got a powerbag for christmas and I absolutely love it. You can check them out at mypowerbag.com and amazon. They have some that are made by ful
It has dedicated laptop pocket, iPad pocket, and smartphone pocket. But here's the kicker. It also has a built in charging system with cables. My particular model came with a 3000mAH battery that is capable of charging an iPhone twice or an iPad 1/2 about 45%-50%. There are cables routed through the bag to charge via micro USB, mini USB, and 30 pin iOS , and a spare regular USB port to attach any USB cable. So out of the box this thing can charge pretty much any modern phone or tablet.
The charging system is built into the bag and the batteries are cartridges that can easily be swapped if you order extra. The bag comes with a charging cable that plugs into the outside of the bag and there are LED's to indicate the charge level. Or you can pull out the cartridge and charge it outside the bag. The only downside is the built in cables are a little short so you kinda have to attach your phone and zip it up in the bag while it charges unless you bring an extra cable and plug it in to the spare USB port on the inside of the bag.
Once I realized the new iPad had a much larger battery I quickly ordered the upgraded 9000mAh battery cartridge that is capable of a (theoretical) 6 iPhone charges.
So now my bag has a 9000mAh battery and I use the 3000mAh that came with it as the reserve power. A total of 12000mAh that is good for a (theoretical) 8 iPhone charges and just over one full charge for iPad 3rd gen.
Sorry for the long write up, but I really love this bag. I often pack up my iPhone and iPad in it for commuting on my motorcycle. It sort of acts as my "car charger" when I'm on my motorcycle. Also great for camping or any other situation where you would want to keep your mobile devices charged up but wont be near power outlets.
The only thing is the markup is a little high. The model I have is the "Backpack by ful" which lists for $139.99 on their website. However, you can get the same model on Amazon for $89.99!!! for that price its worth it, I can say that they are well made and I have never had a backpack that was more comfortable to carry.
Unfortunately I could not find the extra batteries on Amazon, I paid $59 for the 9000mAh cartridge. Mine came with the 3000mAH, some models come with a 6000mAH.