Researchers have invented a new type of battery that has the potential to revolutionize wearables. The tiny batteries can work together in a flexible group, paired up with solar cells to maintain charge, which could open up a range of possibilities for flexible tech that can wrap around the body. The batteries could even work underwater.

“The components are electronically connected via flexible copper-polymer interconnects, mounted on a highly elastic silicone core, and enclosed within a silicone shell,” the team said in a press release on EurekAlert. “The resulting system could stretch up to 30% without detectable loss in solar power generation.”

The team have explained their findings in a new paper titled “Soft, thin skin-mounted power management systems and their use in wireless thermography.” The paper, announced on Monday, has been published in the scientific journal PNAS and was contributed by John A. Rogers from the University of Illinois at Urbana-Champaign.

The findings have potentially major implications for wearable tech and the quantified self movement. Instead of having to wear a bulky wearable like a Fitbit or Apple Watch, users could wear something as inconspicuous as a pair of socks to keep up with their body’s workings.

“The authors demonstrated the use of these systems for continual logging and wireless transmission of body temperature data in a variety of realistic scenarios, such as monitoring skin temperature during physical exercise and bathing, and measuring temperature changes during breathing,” the statement reads.

Because of their flexible silicone and copper structure, the batteries are able to wrap around something as tight as a finger. An expansion of this technology could see the debut of “smart rings” that stretch to fit the wearer’s finger while still measuring body temperature and fitness signs.

The idea of even smaller wearables is something companies are exploring even today. Ringly is a company that specializes in smart rings, bringing notifications to the finger in a similar way to smartwatches like the Pebble. [Apple](http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=46&p=1&f=G&l=50&d=PG01&S1=(345%2F173.CCLS.+AND+20151001.PD.) has also filed a patent for a wearable “smart ring” that could house a touchpad, allowing for interaction with a larger device simply by running a thumb over the ring.

Photos via Jung Woo Lee et al./EurekAlert