In a few years, charging up a smartwatch could be as easy as taking a walk.

This week, researchers at MIT revealed their latest innovation in battery technology: a stamp-like, flexible battery that charges itself just by bending.

Sangtae Kim, a PhD candidate in materials engineering who helped develop the tech, says the bendy battery works best with normal, human-scale activity, like walking, poking, and bending. That makes the technology a potentially perfect fix for charging something like a smartwatch.

You don’t need to be a stellar athlete to make the tech work: walking, jogging, or running, the frequency of bending doesn’t matter. But, “if you run, you’re pressing harder,” Kim says. “That will make the charging go faster.”

This battery prototype charges itself by bending, which could make it an ideal fix for charging wearable tech with human movement. Sangtae Kim, Soon Ju Choi/MIT


The battery hasn’t been perfected just yet, though. The rubbery prototype that Kim and his colleagues spent two years developing is about one tenth as powerful as it would need to be to charge something like a watch or a phone.

“I think it’s quite doable within a year or so,” Kim said.

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If the group can develop a more powerful prototype, the tech could make digital smartwatches operate more like old-fashioned kinetic watches: you move, it charges, about as fast as by a USB cord. That could be a big plus in a market that’s hyper-focused on battery performance.

First, the team will have to test it out. They say they’ll spend this year trying to build a device that is self-charging. One idea is for a baby-monitoring GPS-locator; as a toddler crawls around, the batteries on the locator charge, so parents never have to plug them in.

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Since the group’s paper was released in the journal Nature Communications on Wednesday, they’ve been fielding calls from tech companies eager to learn more about the potential new battery. Kim says there are already two companies interested in working with them, both in wearables and smartwatch markets. And while there’s already tech available that harvests energy from faster motions, like the shaking from a washing machine, Kim’s pleased his group might be the first that’s found a way to get batteries to charge… at the speed of people.

Correction (Jan. 10): The original version of this article failed to give the full name for the journal that published a paper about bendable, rechargeable batteries. It is Nature Communications.