Battery technology continues to improve over time, and manufacturers are making advancements that allow them to pack more power into smaller spaces. The need to provide power to devices more efficiently constantly increases due to evolving internal components that are more demanding with each generation. Aside from batteries growing in capacity, a new technology is in development, which will allow devices to generate energy using body heat.
Daryoosh Vashaee, a professor of electrical and computer engineering at North Carolina State University, is leading a team of researchers that are working on wearable thermoelectric generators (TEGs), which take advantage of heat that is generated by the wearer's body to generate electric power. It is also superior to heat sink technology, which is much bulkier and heavy, making it less practical to wear. Another advantage of wearable TEGs is that they are able to generate as much as twenty times the power of heat sinks (up to 20 µW/cm2). It works by placing a thermally conductive material over a layer of polymer, which keeps heat from escaping, and forces it through the TEG. The material is only 2 mm thin, and flexible. This is not enough energy to power larger devices such as phones and tablets, and it won't power a wearable device in itself, as the device will use power faster than a TEG is able to charge it. However, it could serve to slow down the power consumption process, extending the amount of battery life that a wearable device gets from a single charge, and the number of days it can be worn before the user has to recharge it.
Larger TEGs can generate more electricity, but may also be a bit less practical, as they would take up more space. One possible option is to integrate the technology into clothing. NCSU has already tried this with a shirt, and it was able to produce 16 µW/cm2 of energy. This could become an important selling point for future smart clothing products, such as Levi's upcoming Jacquard Smart Jacket. The ultimate goal is for wearable devices to be able to run continuously without having to depend on batteries, and the technology is not quite there yet, but this is a big step in the right direction. It may not be long before wearable devices are powered by those wearing them rather than by batteries.