Maybe it’s happened to you. You’re tracking a workout on your Fitbit, and mid-way through, the battery goes dead.

Scientists at the Center for Wearable Sensors at UC San Diego are trying to make this a thing of the past. They've created a flexible skin-patch that uses sweat in place of batteries to power small devices with a Bluetooth connection.

According to co-director Patrick Mercier, many wearable devices like a Fitbit end up “in the sock drawer” because people just don’t want to spend time charging them.

“People start to wear them, and they think the information that’s being generated is useful, but then we have to recharge these things all the time," he told KPCC.

The biofuel patch attaches to your arm and is just a few centimeters wide. It has enzymes that replace the metals typically found in batteries. Mercier says they feed off the energy in lactic acid and glucose found in your sweat to power wearable electronics.

“We’ve never been able to demonstrate that with a small wearable energy harvester, so that’s really a key accomplishment of this research," he said.

Mercier thinks this biofuel cell technology can soon be used to power your smartphone and eventually help monitor chronic health conditions like diabetes.

But the lab isn’t stopping there. Mercier's team is also working to use the power of sweat to track glucose and lactic acid levels - things that would make it easier for elite athletes to track their health during competition and training.

“If we could monitor that on a real-time basis, this would be huge for the athletic industry," Mercier said.

Mercier says he’s currently in conversation with Tour-de-France cyclists and the U.S. Olympic Committee about the future applications of this technology.