Battery Power Tips

  • Home
  • Markets & Applications
    • Automotive
    • Aerospace & Defense
    • Energy Management & Harvesting
    • Industrial
    • IoT
    • Medical
    • Renewables & Grid Connected
    • Robotics
    • Stationary Power
    • Wearables
  • Learn
    • eBooks/Tech Tips
    • EE Training Days
    • FAQs
    • Learning Center
    • Tech Toolboxes
    • Webinars & Digital Events
  • R&D
  • Resources
    • Design Guide Library
    • Digital Issues
    • Engineering Diversity & Inclusion
    • LEAP Awards
    • White Papers
  • Engineering Training Days
  • Advertise
  • Subscribe

Don’t rush to choose rechargeable batteries…at least, not yet

By bschweber | November 22, 2021

Using energy harvesting and a rechargeable battery to power a remote wireless IoT node seems like an obvious and straightforward solution, but there are some unique aspects to consider.

Don’t get me wrong: I really like rechargeable batteries; in fact, I like them a lot. Whether based on lead-acid, nickel-cadmium, lithium-ion, or other chemistry, our modern lifestyle – from smartphones to electric vehicles and more – would not be feasible without them. I don’t need to elaborate for you about the usefulness and freedom they provide.

So, when the project requirement is to build a low-power, wireless IoT (Internet of Things) sensor to monitor a physical variable such as temperature or pressure in a remote setting far from any power line, it’s easy to decide on a strategy for powering the sensor-based device quickly. Just set up some harvesting scheme using ambient energy from light, vibration, RF, or thermal differential (to cite a few options), add a small rechargeable battery plus one of the many available power-management ICs, and the problem is solved (Figure 1).

Fig 1: A basic wireless IoT node requires a power-management function to effectively capture and disburse the harvested energy. (Image: MDPI)

But in many cases, that’s short-sighted thinking with a jump to a conclusion. In practice, rechargeable batteries have their own idiosyncrasies and limitations. One of these, which is most easily overlooked, is the number of charge/disengage cycles they can endure before their energy-storage capacity drops by a significant amount.

How many cycles is that? It depends on many factors, but a good first estimate is between 500 and 1000 cycles under ideal conditions. If your system uses daily solar charging, you’re looking at between two and four years.

But “ideal” is not reality. The actual number of cycles is a function of how fully/deeply the battery is charged/discharged in each cycle, the rate of charge/discharge, the ambient temperature, and even the quality of the battery (shhh…). For most Li-ion rechargeable batteries, a general rule (with many exceptions) is that charging to 80 percent of capacity and discharging down to 20 percent yields the maximum number of cycles which is, obviously, a tradeoff against usable capacity.

Then there’s the issue of battery quality. As with most products, there are “better” and “lesser” versions of a given component. You can’t judge the battery quality by looking at its label or making basic measurements, as the factors which determine the performance (materials, manufacturing) are very hard to discern.

A further complication is that even if you specify a higher-quality rechargeable battery from a solid vendor and with the necessary performance, you never know what substitutions will be made by purchasing when offered a better deal. Even worse, there are lots of counterfeits and knockoffs of those better batteries in the supply chain (that’s another “shhh…), so even if you follow the rules and put your chosen vendor on the BOM purchase list with a “no substitution” tag, you could be surprised.

Consider other options

For these and other reasons, designers should also consider supercapacitors (formally known as electrical double-layer capacitors, or EDLCs) as alternate rechargeable energy-storage devices. They have different attributes compared to rechargeable batteries, and whether these are advantages or disadvantages depends on the application (Figure 2 and Figure 3).

Fig 2: This is one perspective of the key characteristics of supercapacitors and lithium-ion cells; the specifics of the latter vary with different chemistries while attributes both are continually changing as well, due to technology advances. (Image: Battery University via Futurebridge)
Fig 3: A broader comparison of energy/power sources shows their energy and power densities as well as charge/discharge times. (Image: Kemet Electronics Corp.)

A way to get the best of both the rechargeable battery and supercapacitor attributes is to consider using both with appropriate charge/discharge management. This can be done by using one of each with appropriate management. Still, there’s another fairly new option from vendors such as Kemet and Taiyo Yuden: the lithium-ion hybrid capacitor.

This component is not just a repackaging of two disparate functions in a common enclosure. Instead, it is a complete re-design of both the rechargeable lithium battery and the supercapacitor from a fundamental materials and chemistry perspective, thus creating an entirely new component which has the characteristics of both.

Finally, there is another factor about energy harvesting that is hard to quantify. The energy source you expect to have available to harvest may not always be there. Sure, the Sun will be there, but will it be able to illuminate that PV cell? Tree grow, buildings are built, and people move things; the same long-term concerns apply to other harvestable energy sources. In short, the physical situation of the harvesting transducer may change over time through human or natural actions. Further, the harvester transducer may have a limited life as well; it could develop microcracks due to constant vibration or shock and eventually fracture.

Sometimes, you really have to step back and do a broad reassessment of the situation. While rechargeable power sources seem attractive – and they certainly are in many cases – sometimes a non-rechargeable, long-life Li-ion battery is a more reliable solution.

You can’t use just any Li-ion battery here, even a “better” one. Standard high-performance bobbin-type lithium thionyl chloride (LiSOCl2) batteries have a self-discharge of around 3 percent per year, regardless of load – even with no load. After 30 years, these batteries will have exhausted up to 90% of their original capacity. After you factor in the average annual current used to operate the wireless device, these batteries can fall below their threshold for usable capacity in less than ten years.

Fortunately, there is an alternative here as well. Vendors such as Tadiran offer non-rechargeable LiSOCl2 batteries, which, due to their material and manufacturing process, have an annual self-discharge rate of 0.7 percent per year. After 30 years, this battery will retain nearly 80 percent of its original capacity.

Conclusion

As usual, the answer to the engineering question is “it depends.” In this case, that question is, “what power source should I use for my wireless IoT?” Don’t assume that a rechargeable battery is the right or only answer, although it certainly may be. Determining the optimum answer requires weighing relative project priorities, risks, and other factors before making the decision.

 

You may also like:

  • battery safety standards
    Battery safety standards and testing

  • 18650, 21700, 30700, 4680 and other Li-ions – what’s the…

  • The difference between primary and secondary battery chemistries

  • How to read battery discharge curves

  • The difference between lithium ion and lithium polymer batteries

  • Introduction to batteries and their types

Filed Under: Applications, Batteries, Battery types, FAQs, Featured, IoT, lithium-ion, Wireless
Tagged With: FAQ
 

Next Article

← Previous Article
Next Article →

“battery
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for EE professionals.

Featured Contributions

  • Preparing for sodium-ion battery storage? Advanced simulation models can help
  • Q & A: why automation is essential for advancing EV battery manufacturing
  • Battery and charging innovations driving electrification
  • What is a lithium battery digital passport?
  • Battery testing: critical to the rise of electric vehicles
More Featured Contributions

EE TECH TOOLBOX

“ee
Tech Toolbox: Internet of Things
Explore practical strategies for minimizing attack surfaces, managing memory efficiently, and securing firmware. Download now to ensure your IoT implementations remain secure, efficient, and future-ready.

EE LEARNING CENTER

EE Learning Center

ENGINEERING TRAINING DAYS

engineering

RSS Current EDABoard.com discussions

  • High Side current sensing
  • Can anyone provide a guide or tutorial for Candece simulation?
  • How to simulate power electronics converter in PSpice?
  • Spreading unwanted heat around
  • ISL8117 buck converter blowing up
“bills
Battery Power Tips
  • EE World Online
  • Design World
  • Medical Design & Outsourcing
  • Solar Power World
  • The Robot Report
  • Contact
  • Sign Up Enews

Copyright © 2025 WTWH Media LLC. All Rights Reserved. The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media
Privacy Policy | Advertising | About Us

Search Battery Power Tips

  • Home
  • Markets & Applications
    • Automotive
    • Aerospace & Defense
    • Energy Management & Harvesting
    • Industrial
    • IoT
    • Medical
    • Renewables & Grid Connected
    • Robotics
    • Stationary Power
    • Wearables
  • Learn
    • eBooks/Tech Tips
    • EE Training Days
    • FAQs
    • Learning Center
    • Tech Toolboxes
    • Webinars & Digital Events
  • R&D
  • Resources
    • Design Guide Library
    • Digital Issues
    • Engineering Diversity & Inclusion
    • LEAP Awards
    • White Papers
  • Engineering Training Days
  • Advertise
  • Subscribe