To make the battery, Lee and his colleagues soaked a piece of paper in a solution of copper chloride and sandwiched it between strips of magnesium and copper. This sandwich was then laminated between two sheets of transparent plastic.
When a drop of urine is added to the paper through a slit in the plastic, a chemical reaction takes place that produces electricity.
The prototype battery produced about 1.5 volts, the same as a standard AA battery, and runs for about 90 minutes. Researchers said the power, voltage, and lifetime of the battery can be improved by adjusting the geometry and materials used.
Urine contains many ions (electrically charged atoms), which allows the electricity-producing chemical reaction to take place in the urine battery. Other bodily fluids, such as tears, blood, and semen, would work easily as well to activate the battery.