How many batteries can IoT really handle?

In the discussion about sustainable technology, there is one thing that often slips through the cracks: the batteries. Not the big lithium batteries, but the small cells hidden inside IoT devices. During Robert Forchheimer’s keynote at IoT World in May, he mentioned that 78 million batteries are replaced daily, referring to a 2021 projection (Robert emphasized he wasn’t certain of the figure).

IoT depends on small batteries

To draw attention to the widespread use of disposable batteries—so-called primary cells—I shared the figure of 78 million in a LinkedIn post. Several comments pointed out that the numbers didn’t match reality, and many defended primary cells. I can admit the figure perhaps should have been questioned more, but my intention with the post was never to make that number the main point. It was to highlight a bigger issue: our dependence on primary batteries, and how rarely energy harvesting is used.

What is an IoT device?

To understand how many batteries are consumed globally, we have to make a few assumptions. The number of active IoT devices worldwide is difficult to know exactly, but it can be estimated at over 15 billion—a figure supported by data from IoT Analytics and Statista.

How many of these are battery powered? No one knows for sure. But in many applications, primary cells are the standard solution. It’s simple and cheap. The fact that they later need to be replaced is often not included in the total cost of ownership or environmental impact calculations—it becomes “someone else’s problem.”

My own home alarm sensors need new batteries about every eighteen months. My AirTags last a few months. On the other hand, industrial sensors often claim ten years of battery life—at least if you believe the manufacturer’s data.

Battery replacements happen more often than we think

If we assume that half of all IoT devices are battery powered, we’re talking about roughly 8 billion devices that run on batteries. With an average battery lifespan of five years, that means 1.6 billion batteries must be replaced each year—or just over 4 million per day. In reality, many devices have shorter lifespans, and some use multiple cells. It’s not unreasonable to estimate that global daily consumption is closer to 8–10 million batteries per day—not 78 million, but still an enormous number.

Primary cells often end up in the trash

The most common batteries in IoT offer long life, but in practice are rarely recyclable. Around 15 billion alkaline batteries are sold globally each year, according to Avicenne Energy (2022). That makes batteries for IoT a significant share of the world’s total battery consumption. Unlike batteries in phones or laptops, primary cells are not rechargeable and risk becoming electronic waste—or worse, being improperly discarded—once their service life is over.

Energy harvesting should be the standard by now

Even though the technology isn’t new, it’s still rare to see IoT devices powered by energy harvesting—that is, devices that generate their own energy from the environment. There are several working technical solutions, and many are mature enough for practical use. Yet they remain largely absent in the field. One has to wonder: why?

Four technologies that harvest energy

Solar energy – Solar cells are the most proven option, especially for outdoor environments. The technology is at times costly, difficult to scale (dark and cold in Sweden during winter), and requires well-thought-out installation. For indoor use, traditional solar cells are often too inefficient—the light levels are simply too low. But the new generation of indoor solar cells has made significant progress. They can generate enough micro-power to run BLE sensors, motion sensors, or other low-power systems. The challenge is that energy availability varies greatly over time, and energy may need to be stored.

Piezo and vibration – In environments with motion—like doors, machines, or push buttons—energy can be harvested using piezoelectric technology. There are companies that have built entire ecosystems based on this principle. The technology works by pressing a button, for example, to turn off a light. That motion stores energy to be used for the next press.

In constantly vibrating environments, energy can be used to provide continuous sensor operation, but the technology is still relatively expensive.

Radio waves – We’ve heard about harvesting energy from radio waves, but in practice, it yields very little under most realistic conditions. A typical WiFi router emits only a few microwatts per square meter—enough for an extremely low-power sensor, but not reliable for continuous operation.

Supercapacitors – These are an ideal buffer, far superior to batteries—they charge quickly and tolerate many cycles. In combination with other light-harvesting options, they can be a very promising hybrid solution. However, they require constant energy input and can’t store energy over time like batteries. Performance is also affected by temperature and self-discharge, but that is the case for batteries as well. While batteries discharge under such conditions, the supercaps will revert back to its originial level.

One advantage of supercapacitors is their long lifespan—in some cases over 500,000 charge cycles—which makes them especially attractive in environments where maintenance is costly or difficult. For applications with irregular but recurring energy flow, they can serve as a buffer, making the sensor fully self-sufficient.

Designing for energy harvesting takes courage

So why isn’t energy harvesting used more? The simple answer is: cost, uncertainty, and complexity. To succeed, you need to build systems based on available energy—not desired performance. That often means moving away from established design patterns. Replacing a primary battery is both a technical and strategic shift: you need to understand how much energy can realistically be harvested, how much the sensor consumes—and how energy is stored. On top of that, the hardware becomes more expensive, which is problematic in price-sensitive volume markets.

When we look at rechargeable batteries, certification becomes tougher (I speak from personal experience here). If an IoT device contains a rechargeable battery—especially if it charges via the power grid—more safety standards apply. This means more testing, more documentation—and higher costs.

Batteries can have multiple lives – sometimes

While researching this article, I came across “second-life batteries” as a way to extend the life of lithium batteries, for example from electric bikes. Some companies show that it is possible to give lithium-ion batteries a second life. When batteries are needed, we should make sure to maximize the use of each cell. The challenge? Each cell needs to be analyzed in detail.

The solution could be automated testing equipment capable of validating thousands of cells per day—a prerequisite for scaling this. There are systems where customers subscribe to battery capacity. When one module performs below the promised level, a new one is sent out, and the old one goes back into the test cycle—a circular process where each cell can live three, four, or more times before being finally recycled. Other experts warn against relying on second-life batteries without in-depth analysis, and argue that even the analysis itself can go wrong. For IoT devices requiring continuous and stable performance, this is not yet a viable option. The use of reused batteries in sensitive applications is, at least for now, out of the question.

We need to start building smarter IoT

We need both companies and customers who go against the grain and demand energy-smart systems. Unfortunately, many still choose primary cell batteries because they feel like the “safe” option—both in terms of cost and development—despite the fact that they result in higher environmental costs and increased maintenance complexity over time. In the long run, we must ask ourselves if we should even build battery-dependent IoT at scale when energy harvesting is a real, available alternative?

It’s also a matter of mindset—of daring to question established norms. One big challenge lies in convincing the market: how do you sell a used battery cell with confidence? How do you build a device that harvests light?

Developers often oversize batteries or choose primary cells by habit. But that’s a barrier we can overcome—and we should start now.