MetalCell - a Battery That Runs on Urine

Imagine you are cut off, alone, and out of juice (power). All you have are a few beers and a dead flashlight/phone. Now what? If you are packing a MetalCell, drink the beer, give it a few minutes, and then pee on the device. Your urine can keep the voltage flowing for hours. Salt water works to. The sodium reacts with the magnesium plates to produce low voltage power. If you start running low, you can power it back up by peeing on it again. The device can be left in storage for years and will continue to work until the magnesium plates deteriorate.

http://www.popsci.com/technology/article/2010-04/portable-battery-runs-saltwater-%E2%80%93-or-urine (Via)

"Fitted with magnesium plates inside, the MetalCell can be charged up with nothing more than the addition of saltwater. The sodium in the salt reacts with the magnesium to create a dose of low-voltage power that can power up laptop, a flashlight, night vision specs, etc. when no other source is available. The output can keep a laptop humming for more than four hours and can be recharged with fresh saltwater until the magnesium begins to deteriorate.

Soldiers can pool salt from their Meals, Ready-to-Eat (MREs) to create the a proper sodium solution, but failing that, soldiers could also charge up the MetalCell with their urine (and given the blandness of MREs, they might opt to). That's an energy-rich resource a grunt can always lay his hands on."