After trying many different batteries and power-packs for my iDevices, I have chosen the Newtrent PowerPak NT100H. Clocking in at 10,000mAh, almost 4 times the capacity of most others, the PowerPak has enough power to fully charge your iPhone & iPad more than once. It also features a port for designed specifically for your iPad (2.1A), which allows fast charging. A second 1A port for your iPhone is also available. The Newtrent PowerPak is very simple to use. It features a one button status check which give you the current charge amount.
It is also styled very nicely. The slick black case has resisted scratches even though it has been in my travel kit among several metal objects. This is a must have for any traveler.