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Water-powered calculator

Great! A water-powered calculator using patented water battery technology, and sold as an environmentally friendly solution to all those non-rechargeable batteries. "No batteries, no electricity, just add water!" gushes the blurb. This must be a real breakthrough on a par with the invention of a perpetual motion machine. You can see the battery neatly integrated into the design of the calculator.

water-powered calculator

Let's look at these water batteries in more detail:

The way they are being sold suggests that the power source is somehow water – giving an inexhaustible supply of energy. Well, as a fuel technologist I have some bad news: you can't burn water – it's already been burned.

These batteries work on the same principle as any other battery: two electrodes and an electrolyte. In this case the electrolyte is water. The electrodes are some alloy or other that will react and dissolve in the water over time to generate the electricity. Because the power consumption of LCD devices is so small those electrodes should last a long time, but not indefinitely, hence the stated lifetime. The product offers the "freedom of not having to buy batteries again", but the manufacturer also has replacements are available, if a little pricey. I have a pocket calculator that has used the same tiny mercury cell for over last twenty years. Over that period I could expect to have tossed at least half a dozen or so of these "green" batteries.

Verdict: If you want a fun gimmick; great. If you want to go green; get a solar cell calculator.