How much power to fully charge a dead Surface 3 battery?

[netuser]

Since it charges over Micro-USB, seems like you should be able to recharge with one of those portable "juice packs" like they make for cell phones.
That would be very convenient, because you could recharge the Surface hidden away in your bag and not plug into a wall outlet until you get home. If they juice pack is slim, it would easier to carry in a slim bag with the tablet than the blocky, protruding power adapter that comes with the Surface.
However, a Surface 3 would require much more power to recharge than any cell phone.
How much juice would a Surface 3 need to recharge and do manufacturers make juice packs that would recharge it fully or even add more than 50% of a recharge?

 

[Korruptor]

Yes, you can use one of those juice packs. I have a PowerAdd 20800mAh battery pack, which works great for me for my iPad Air 2, phone, plus other devices and still not be empty.

If you're in the USA, I got it from here and it's currently $34, which is an excellent price
http://smile.amazon.com/Poweradd-Pi...032&sr=1-8&keywords=poweradd+portable+charger

20800mAh is a LOT, but I really don't know how much the Surface 3 has. I'll try it out shortly after I get my Surface 3, but I think the battery charger should be able to fully charge it.