Tired of your cellphone dying during an important call or your car not starting on a cold morning? Researchers at Princeton think you should listen to your batteries.

“How sound moves through a battery indicates important things about the battery’s internal structure,” said Daniel Steingart, an assistant professor of mechanical and aerospace engineering and the Andlinger Center for Energy and the Environment. “It can show the level of charge and also how the battery is and what has happened to it over its lifespan.”

A team led by Steingart is using sound waves to track batteries’ internal health in real time. The scientists believe their technology will offer a new way for researchers and manufacturers to peer inside batteries and monitor their structures as they discharge. The technology also could eventually be developed into a system that monitors batteries in critical situations such as medical devices or massive systems that store and release energy from wind and solar collectors.