Your future phone may never need to be charged.

That's the exciting implication of new research out of the University of Washington, where researchers have created a mobile phone prototype that doesn't require a battery to operate.

The astonishingly efficient prototype requires just 3.5 microwatts of juice, and it employs an innovative approach to avoid the need for a battery cell. Instead, it uses ambient power from radio signals and light — its onboard solar cell is "roughly the size of a grain of rice" — to transmit a signal back to a base station 50 feet away.

The prototype itself is made of simple materials: capacitive touch buttons, a circuit board, and other "off the shelf" components. More impressive is that the team of scientists were able to create a custom base station to transmit the signal with such a small amount of power.

Using this setup, the researchers were able to successfully make and receive calls (via Skype) and place callers on hold. But the scientists say they want to improve the prototype by adding an e-ink display with video-streaming capabilities and encryption to make the calls more secure.

Vamsi Tall, who coauthored the paper, says the base station technology they developed — while it's still an early prototype — could make it possible for battery-free mobile phones to become ubiquitous.

“You could imagine in the future that all cell towers or Wi-Fi routers could come with our base station technology embedded in it,” Tall said. “And if every house has a Wi-Fi router in it, you could get battery-free cellphone coverage everywhere.”