Selecting the best lithium primary batteries for your LoRaWAN node

Cecile Joannin

The Things Network User

Posted on 12-01-2021

Battery lifetime is a key factor influencing the success (or failure!) of an IoT solution. Indeed, replacing batteries when your LoRaWAN devices have already been deployed in the field for several months can represent a huge operating cost that can jeopardize the ROI of your solution. The question is not only how to get the maximum lifetime from your battery but how to obtain an accurate assessment about it in real field life conditions. Thus, understanding which factors affect the battery’s capacity is paramount to be able to leverage the risk linked to a battery failure.

The lifetime of a battery depends on several different parameters: firstly, there are parameters linked to the IoT use case itself. Then, the electronics design technical choices will greatly influence the consumption profile of the device, and therefore, the battery’s capacity. And finally, although they can be similar technologies, the battery’s lifetime will depend on the know-how and secret recipe of each brand and manufacturer!

What is the influence of your use case on the battery selection?

The IoT use case will determine:
1. The type of communication solution (LPWAN technology, radio communication or cellular solution ?) that will be used, and therefore, partially, the consumption profile of the application.
2. How frequently the end-user needs to retrieve the data from its sensor or tracker, which will greatly impact the energy needs, and accordingly the battery life.
3. The geographic zone in which the solution will be deployed: if the devices are to be installed outdoors, it will impact the temperature conditions of the battery, which is one of the main influences on the battery’s behavior and longevity. The geographic zone may also imply a specific telecom infrastructure and commercial availability, which is also of importance in the device’s energy consumption.

To help you to discover which battery can match your IoT application and what impacts the battery’s lifetime, you may want to try Saft’s IoT Smart Selector, a free online tool that enables you to find the best matching battery solution in just 7 steps.
Saft's IoT Smart Selector
In order to maximize your chances to start with the right battery assumption, you will therefore have to first of all carefully define your use case (which will also be important for the rest of your project!).

What about the electronics design of my IoT solution?

The technical choices you will make during the design of your solution will greatly influence the battery’s lifetime! At this stage of your development, several tools and tips can allow you to optimize your electronics design for the lowest consumption and/or the maximum battery’s lifetime, as explained by Wisebatt in their article, and there are several solutions that can lead you to reduce the energy needs of your device.

But limiting the evaluation of the battery’s lifetime exclusively to its energy aspects is a common pitfall: a lithium primary battery is not a constant voltage generator! Therefore, the voltage response of the battery must be considered and must remain above the cut-off voltage throughout the application’s expected lifetime, to avoid premature failure. This is why we consider the cut-off voltage of the application you have designed as a crucial factor for the battery selection, which will also determine the battery’s available capacity. If you’d like to find out more about it, watch our series of videos and the article “5 tips for IoT systems developers at the design stage to follow when deciding upon a battery for your connected object”.

In order to assess the selected solution’s lifetime, now that the use case and the electronics are known, we have to identify the energy-consuming functions considering the expected behavior of the device: sleep and standby modes, listening and transmitting modes, without forgetting all the leakage currents of all components. We also need to explore the levels and duration of the pulse and how often the data will be transmitted to get the full picture of the energy needs. This, and much more, can be achieved by measuring your prototype’s real consumption with Qoitech OTII and Battery Life Estimator.

At this point of your development, once the consumption profile of your electronics and application are well known, you will need to get in touch with your battery manufacturer to obtain a confirmation of your battery selection and an accurate lifetime calculation of your solution.

If you want to deepen your knowledge about the way Saft is calculating the lifetime of battery solutions, particularly for connected applications, you can check our blog article: “How can primary batteries achieve their expected lifetime?” .
What influence the battery longevity of an IoT application?
Finally, You can get in touch with one of our experts to get a battery recommendation or lifetime calculation. Feel free to email us at energizeIoT@saftbatteries.com. We will be happy to help!

Learn more about battery selection for IoT application at the LoRaWAN event of the year, online on Jan 25-29, 2021. Jean-François Savin, application engineer at Saft Connected Energy, along with a team of experts from Qoitech, will be delivering essential advice during a practical workshop.

Register today and use our discount code: TTC2021-FRIEND-OF-SAFT

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