The ZMI PowerPack 20000 is the most useful backup battery you can buy. It packs a huge, 20,000mAh battery that can power a MacBook and two other devices at the same time. Plus, you can quick charge it via USB. And it can even work as a USB data hub.
This 14.29-ounce (405 gram) brick might be overkill for daily juicing of your iPhone, but for everything else it’s amazing.