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METAIRIE, La. —  First, the survivors of Hurricane Irma were just glad they were alive.  Then, they wanted to charge their phones.

A gadget designed by a Florida inventor won’t keep a refrigerator cold or the lights on, but it will generate enough juice to turn on a laptop or charge a cell phone– two things that might be essential when the power gets knocked out.

Allan Riggs calls his device the “GMAG Power Cell” and he sells them at “survivalist” conventions to people worried about communication after a hurricane (or, lately, after a North Korean bomb).

The “G” in “GMAG” stands for “green,” or “clean” energy.  Riggs says he uses recycled plastic. The “MAG” stands for magnesium.  And this is where a little high school chemistry can come in handy.

Riggs’ pitch is that all you need is about a teaspoon of salt and a quarter cup of water (or in a pinch, some of your own urine) to generate power.  But there are actually two more links in his power supply chain — magnesium and batteries.

It works like this:  A pod of magnesium about the size of your palm is attached to six double “A” batteries.  When the magnesium comes in contact with saltwater, it creates a chemical reaction that will charge (or re-charge) the batteries.

Riggs says that’s what makes the GMAG a portable and almost indefinite power supply for small items like cell phones.

Riggs describes himself as a retired Navy man, “an electronics kind of guy,” who’s been tinkering around with his invention for years.

He says the idea started as a way to power remotely-operated undersea vehicles using marine batteries.  That led to a patent for his “self-charging battery.”

“I get excited just talking about the possibilities,” Riggs says.

“Think of all the underdeveloped countries that could (use) my GMAG Power Cells to provide power to families… where there currently is no power…  We can help.”