Scientists have created a skin patch that can power a radio for two days using human sweat, and may eventually be used to charge mobile devices while people are out for a run.
The bio fuel patch may also provide a way to monitor glucose levels in people with diabetes, without needles and blood samples, researchers said.
The skin patch developed by researchers from University of California, San Diego in the US is a flexible square just a couple of centimetres across and sticks to the skin.
It contains enzymes that replace the precious metals normally used in batteries and uses sweat to provide power.
Getting enough power out of a bio fuel cell to make it useful has proved tricky, but the latest version can extract 10 times more than before, researchers said.