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The first urine-powered paper battery has been created by physicists in Singapore. The credit-card sized unit could be a useful power source for cheap healthcare test kits for diseases like diabetes, and could even be used in emergency situations to power a cellphone, they said. Testing urine can reveal the identity of illnesses, and the new paper battery could allow the sample being tested to also power the diagnostic device. The urine-powered battery was able to generate a voltage of about 1.5 volts - with a corresponding power of 1.5 micro-watts - using just 0.2 millilitres of urine, said Lee. And if a second droplet of urine was added 15 hours after the battery was first activated, the replenished urine could generate still more electricity. The battery is made of a layer of filter paper steeped in copper chloride, sandwiched between strips of magnesium and copper. This "sandwich" is then laminated in plastic to hold the whole package together. The resulting battery is just 1 millimeter thick and 60 by

30 mm across - slightly smaller than a credit card. To activate the battery, a drop of urine is added and soaks through the sandwiched filter paper. The chemicals dissolve and react to produce electricity. The magnesium layer acts as the anode, losing its electrons. And the copper chloride acts as the cathode, mopping up the electrons. He added that the voltage, current and capacity of the battery could be improved by different designs or by switching the electrode or electrolyte materials used.