The rugged little boxes are similar to the so-called Baghdad batteries dating to the early centuries A.D. that some researchers believe were the first voltage-creating devices. 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.