If you've got an electronic device, you need power either in the form of a cable or a battery. If you've got a battery, you still need a means of charging it. And if you're in the military, you know that you never have exactly what you need exactly when you need it. Which is why South Korean battery makers have created the MetalCell, a magnesium battery based on 2,000-year-old technology that can be charged with saltwater or, barring that, urine.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.