like the integrated cable - I have bought 2 NewTrent external powerpacks over the years (I lost the first one).
Also available on Amazon, and they are often heavily promoted. They are good quality, and have a huge range of capacities available. Though unless you are planning going into the jungle for a week, I would get something in the 3-4,000mAh range.
That is 1-2 days' heavy use, and since capacity is lineally proportional to size and weight, you get that capacity for about the same size as a normal smartphone.
Nexus 4, ROM: Pure Speed X 27/11/13 build