We really like the idea of eco-friendly water-powered gadgets. Exhibit A: the H20 desk calculator. Add a few drops of tap water to the removable battery and put it back in the product for up to three months of use. When the display begins to fade, just make another trip to the sink.
This isn't the only water- or electrolytic-liquid-powered calculator around, but online seller Solutions notes that the battery in this one can be taken out, stored in a dry state indefinitely, and activated when needed. It can be "re-energized by the addition of water again and again," supposedly lasting a lot longer than alkaline batteries.
The calculator has a standard 12-digit display and takes care of your basic adding machine functions. It sells for $24.95, which seems more than reasonable if promises of an Energizer Bunny-type battery persistence bear out.
Readers, have you used an agua-powered clock, calculator, or other gizmo? If so, how did it work? Are H20-powered cell phones and MP3 players next?