Batteries made of lithium metal are preferred over lithium ion technology, but because lithium metal reacts with water. But it hasn't really made any sense to try to use it until now. One California-based company called PolyPlus created a lithium-water battery that is making quite a splash. The underlying technology is a bit counter-intuitive, considering lithium reacts violently with water. To get around this though, PolyPlus found a way to protect the lithium metal with a membrane, so the ions could slip through and maintain a charge. ARPA-E director Arun Mjumdar describes the new water battery technology as.. a fish in a glass tank. For demonstration purposes at the ARPA-E conference, PolyPlus put the membrane-covered lithium pack into a glass of water and showed that it could produce enough energy to make an LED light glow. The technology works like this: The battery reacts with the oxygen that is dissolved in water. And you know what? The water battery can produce 1,300 watt-hours per kilogram of electricity, according to Scientific American.