Everyone has felt the pain of a device running out of power just when you need it the most.

That pain point is fueling research on dozens of inventive charging technologies, but one group of researchers at the University of Washington is taking a different approach: get rid of the battery altogether.

The group unveiled its battery-free cellphone, which uses energy from ambient light and radio waves, in a recent paper. Although the current model is still a prototype, the group has passed the biggest hurdle in making the technology a reality: converting analog sound signals into digital signals that a phone can process.

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