By a wide margin, Sanho's HyperJuice Plug 15,600mAh ($160) is the highest capacity external battery pack we've received for review. Not surprisingly, it's physically pretty huge: 6.1 x 3.4 x 0.78 inches, and weighing in at a little over a pound. Rather than relying on extra cables for charging the battery itself, Sanho built in slide-out prongs that fit directly into a power outlet; because of the weight, it seems wise to use the lower outlet and…