The battery is powered by chemical energy stored in the battery; the water just kicks off the chemical reaction. The calculator doesn't say, but I'd guess it's powered by a thermocouple with one end cooled by the evaporation of the water inside - calculators need very little energy to run. In both cases "water powered" is a bit misleading to say the least.
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timeasmymeasure
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Date: 2008-07-22 02:53 pm (UTC)