If you need a big external battery for traveling, camping, or to have around in case of an emergency, then listen up. Amazon has the Omaker 15600mAh Portable Charger Power Bank (and that's the abbreviated version of the product name, whew) with dual 2.1A output USB ports on sale today for $22.99 after applying a coupon code. That's a whole lot of mAh's for not a lot of money.
As far as power banks go, the Omaker is a pretty handsome device. Its grey outer shell is plastic, but has the look and feel of powder coated metal. A thin strip of either blue (or orange) contrasting plastic runs down the length of the device and forms the caps on both ends. User's reviews state that it is hard and rugged and withstands a moderate amount of abuse easily.
The battery recharges from empty in 7-8 hours and carries enough juice to refill most modern smartphones 3-4 times and a tablet 1-2 times. The main selling point for me is the speedy 2.1A output which should charge your phone at about the same rate as a standard wall charger. The unit also features a four bar LED battery status indicator and pass-through charging capability (meaning you can charge the battery while the battery is charging your phone). The inclusion of two USB to MicroUSB cords and a drawstring carry bag is a nice bonus. The only possible negative I see is that it does not have an LED flashlight on it like many other power banks of this size, but that is hardly a must-have feature.
Omaker's products carry a 12 month warranty and this model has a 4.6 star rating with over 100 reviews, so you should feel secure with your purchase if you choose to pick one up. Don't forget to enter the code 11OMAKER (that's a letter o, not the number 0) at checkout to drop the price by $7 to $22.99.