In 2005, Singapore scientist King Bang Lee and colleagues at the Institute of Bioengineering and Nanotechnology created the credit card-size battery as a disposable power source for medical test kits powered by urine..
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, Lee said.
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.