Thanks to a tip from a reader I found this impressive deal on really well reviewed 20800mAh dual USB powerful battery brick <-LINK. I have not tested this one personally (yet) but love my own 20k brick and use it just about every time I travel. Even though most Delta jets now have power outlets, having spare power is a must for me (I end up on a bunch of CRJ200s sad to say)!
This brick has both 2A & 1A output and even includes a tiny flashlight built in. All very nice and for under $20 is IMO a flat out bargain.
Notice however the one thing that is NOT included is a wall to USB adapter <-LINK so if you do not have one of those you may want to consider one as well. – René