[ta75757]

    Salt water is free.

Salt water is not the point. The anodes and cathodes and the LED lamp are the point.

    corner store to go pick up batteries at

The electrodes need to be replaced regularly. Where will the replacement parts come from? That problem is equivalent to having to "pick up batteries".

    The materials will simply survive better in this 
    environment than traditional batteries, and need to be 
    replenished less.

How do you know this? It doesn't say so on the website that I can see. Are you an expert on batteries (not sarcastic)? I'm not but I'm guessing a lot of engineering has gone into existing battery technology, including batteries for rugged environments and/or long term usage.