At a recent CES show in Las Vegas, I met someone who was developing a smart insole to measure the pressure forces at multiple locations on the subject’s foot. As we discussed the design challenges, she said “The biggest problem is figuring out where to put the battery,” as she showed me a large coin cell. Batteries can hold a useful amount of electricity, but they do pose problems. They tend to be rigid, which can be uncomfortable when worn next to a human body that changes shape with movement. There are flexible battery technologies, but these tend to store much less energy and thus are more limited in what they can do.

There is a third way, however. If you make the rigid batteries small, and then join them together with a flexible connection, you can get the best of both. That’s what researchers at the Fraunhofer Institute for Reliability and Microintegration have done. While working to develop a smart band for a project, they came up with a segmented battery design.  They use tiny lithium-ion batteries fabricated on rigid substrates, and then connect these modules with flexible conductors. The end result is a lightweight, rechargeable power source that is inexpensive to create and that can change shape to adapt to curved surfaces such as a person’s wrist. According to the researchers, the system can store 1.1 watt hours of power which is sufficient to power a typical smart watch (without requiring an internal battery to add bulk to the case).

This approach could deliver more power over a longer period in a package that is more flexible than standard batteries. This could lead to smaller and lighter wearables for the wrist and other parts of the body. Devices that can run longer between getting recharged will help them “disappear” into our lives, making it more likely that people will continue to use them.