A team of engineers at Arizona State University and Jinan University in China have redesigned the lithium-ion battery to fold, expand and contract, allowing it to stretch and expand to more than 150% of its compacted size even when being used.

The new design uses an extremely common battery and overcomes the tendency for the material to break and tear where it’s been folded and creased by using carefully calculated soft creases, limiting the chance of damage.

Stretchable batteries allow engineers to custom-fit batteries into moveable, flexible devices like a robot’s legs or a wristwatch bands.