Seems like a small niche, but if you need a bag AND a portable battery, it might be for you. For a decent price too.
Powerbag RFAP-0080F 16" 3000mAh Messenger Bag - Black
Yeah, bought one of these last time they showed up on Woot. The battery is nice, but the amperage on the connected cables is lacking, but on the USB port its is fine. All of the ‘smaller’ pockets are completely useless, even the ones that have the cables attached. My Galaxy Nexus would not fit in the pocket.
The main pocket, the Laptop and sub ‘tablet’ pocket all are fine though. The USB port option on the battery makes it really nice to charge an iPad.
Overall a very ‘meh’ product. The sling bag option may be more to your liking.
Powerbag RFAP-0145F 14" 3000mAh Charging Sling Bag
I bought the Slingbag in March 2013. Very comfortable to wear, you don’t really notice it much, and I normally have a hard time with all kinds of bags slipping off of my shoulders.
I’m actually able to fit my 15.6" laptop in the back pocket. There’s enough room in the middle pocket to keep my game controller & a few other items. I had to get a different covering for my iPad for it to fit in the iPad pocket. So if you have a complete case for your iPad, you’ll need to take it off or see about getting just one of the screen covers.
The real problem I’ve found with this bag is the battery won’t stay charged up if you don’t use it for a bit. I’ve barely used it for its charging capabilities, but when I do, the battery is already drained & useless. My phone battery drains pretty fast, so having a charger on hand would be great…if it actually worked.
Within the last week, I attempted to charge my gear while the battery was plugged in & charging - which I have done before - and nothing I plug in will charge. I’ve re-seated the battery, tried all my devices on the attached cables plus tried other cables plugged into the USB port on the charger, and nothing works now. I’ve only had the bag since early March, so I’m kinda upset that even the charging function has already died.
So, it’s a nice bag, just the charging part - the part I really bought it for - is junk. 
I have BOTH the backpack AND the Messenger, and my girlfriend has the sling, so I think this qualifies me somewhat as an expert…
In short, the backpack is great! It holds an enormous amount, and was all I took with me on a recent weekend trip to Boston (2 days, and I’m a BIG guy, so I have BIG clothes)!
Charging system in all the bags is wonderful, as long as you are not planning anything but a smartphone or iPad (Won’t charge my ASUS Transformer TF1-01).
Messenger is a waste of money. Due to the placement of the battery, it is all but useless for anything but a tablet, Mac Air (won’t hold my MacBook), and a THIN notebook or newspaper. Foget lunch - it’s not big enough for a sandwich and apple when fully loaded. Outside “water bottle” pockets are a joke!
Sling is somewhere between the two. Also doesn’t hold much, but it isn’t intended to; a light jacket, tablet, phone, wallet and umbrella is about it. My GF uses hers as a casual, medium purse.
If the backpack is a 10 and the messenger is a 5, the sling is about an 8.
I purchased the Sling the last time these came around, and when it came time to use it I was disappointed. The main failure for me was the space it could hold was TINY.
I ride a motorcycle and thought it would be nice to have as a backup to charge my phone occasionally, but there is just no storage space in it at all. If you are needing to carry ONLY a very small laptop, or ipad, then I could see it being useful, but it truly is designed to carry only what device you plan on charging.
AAAAGGGHHHH!! I was waiting for payday (today) to hit “buy it now” and I missed it by an hour!! I have the messenger but really wanted the backpack. Anyone willing to sell me theirs??? 