IoT device battery selection and optimization is as important as (or perhaps more important than) any other aspect of a battery powered IoT device development. For the simple reason that IoT devices are no good to anyone if they are dead. However, selecting the best battery for IoT devices is easier said than done, because one must walk a tight rope balancing size, cost and device life – all at the same time.
As with most other aspects of a good IoT device development battery selection also has macro factors that most people venturing into IoT are exposed to, and finer details that are in the focus of the professionals only.
Following are some of the parameters we factor in when deciding on a battery for an IoT device.
- Battery Chemistry
- Charge Cycles
- Cell Voltage
- Voltage Stability
- Peak Discharge Current
- Self-Discharge Current
While each of these is a topic deserving a separate article, we explain them in brief below.
Sample Portfolio : IoT Devices
Easily the most important factor in selection of IoT device battery, the battery chemistry, dictates to a large extent the remaining parameters. While there are older chemistries likes Lead Acid, NiCd and NiMh etc., that are still used in many traditional applications. For IoT devices the go to chemistry is almost always primary (One-time use) or secondary (Rechargeable) Lithium based. Following are some of the most popular Lithium based chemistries.
Each of these has its own advantage and limitations. A through understanding of these allows a IoT device battery selection that is most optimum given the application.
Charge Cycles is the number of times a secondary battery can be charged and discharged. For different secondary batteries the charge cycles can vary from a few hundred cycles to about two thousand cycles. Practically speaking this could mean approximately 5x to 8x difference in the overall life of an IoT device.
Cell Voltage and Voltage Stability
Cell voltage varies with the chemistry chosen. Based on the application, choosing the right battery with the right cell voltage can impact the efficiency, complexity and cost of the power circuitry going into the IoT device.
Voltage stability can impact the effective usage of the energy stored in the battery. For example, Lithium Thionly Chloride has perhaps the best voltage stability and almost the entire energy stored in the battery is effectively used because of excellent voltage stability. Such a chemistry also allows for a low cost and simple power circuitry design too, saving further cost.
Peak Discharge Current
The maximum instantaneous current a battery can deliver is the peak discharge current. Some IoT devices require very low yet steady current during the entire life cycle (Example: BLE beacons) and some require very high peak pulsed currents (Example: Cellular IoT devices). A good IoT device battery selection should factor this to ensure reliable operations. Also, in many cases a good circuity design is equally critical for high peak current applications.
Because of the internal chemical process, batteries discharge all by themselves, even when not used. Some types of batteries discharge at a faster rate than others. Common sense implies that IoT devices designed for long life times on a single charge must be powered by batteries with the lowest self-discharge currents.
In addition to these there are certain other factors, that based on the application can become more critical than those mentioned above. Perhaps we will touch upon those in another part. In the mean while for those of you looking to dig deeper we strongly recommend visiting Battery University.