The Internet of Things will be largely dependent on batteries. As the way the charge is taken from the battery is crucial for the battery’s lifetime, SICS Swedish ICT is looking at battery friendlier methods to get the most out of them. Researcher Laura Feeney explains how it works:
Battery drain is not linear
Minimizing energy consumption is very important for the battery-powered devices that will be part of the future Internet-of-Things. Their useful lifetime will be largely determined by the lifetime of their batteries. Today, researchers evaluate Internet-of-Things systems in terms of the total amount of battery capacity that they consume. In other words, they treat the battery as a simple "bucket of energy". But batteries are complex electro-chemical systems and it is well known that the way that charge is taken from the battery affects the amount that can be usefully extracted.
Two particularly important factors are the electric current load and the duty cycle. These properties have been widely studied for the kinds of batteries used in larger and more expensive devices, such as electric vehicles. But the small, cheap batteries, that are likely to be used in Internet-of-Things devices, have not been as widely studied ─ until now.
Making small batteries last longer
Since last year, SICS Swedish ICT researchers have been participating in an intensive program of experiments measuring the discharge behavior of CR2032 lithium coin cells (button batteries) under a variety of loads. Our goal is to develop models that allow us to design not just energy-efficient, but battery-efficient systems, and to estimate their state of charge in real time. We have found, for instance, that a pulse discharge can be much more friendly to the battery than a steady drain, as the battery recovers between the pulses. Also we know that it is more battery friendly to drain it at a lower rate for a long time than at a high rate and rapidly.
“The most exciting part of it is that it is quite new work. There are not a lot of earlier results to guide us, so we can explore and be surprised”, says Laura Feeney, who conducts the research at SICS.
“It is exciting how useful our results will be”, says Bengt Ahlgren, who leads the research group at SICS. “Small batteries’ lifetime is little explored but it will become very important when millions of things start using batteries to communicate with the Internet. It will be very beneficial to the system builders when they know exactly how long a system can be expected to work with a set of batteries in real life.”
Some of this work was carried out in the VINN Excellence Center WISENET, where SICS is a partner. The experiments have been carried out together with Pricer, a company that delivers electronic shelf labeling solutions – a typical Internet of Things application. Uppsala University, and Etteplan Stockholm have also participated in the project.