CR2032 Maximum Current Capacity: Datasheet, Reality, and Alternatives
January 03, 2025
Blog
Consider the humble CR2032 battery. Roughly the size of a quarter and capable of supplying around 225mAh at a nominal 3V, these little coin cells are used to power all manner of small electronic devices that require a small amount of power. One might assume they can easily discharge 10mA or so, to power something like an ATtiny85 microcontroller plus an LED constantly for hours–or much longer intermittently.
This sort of operation and more is possible in practice–e.g. ATtiny85 as a picture display. However, if you check the datasheet for a Panasonic CR2032, its continuous drain is spec’d at just .2mA–insufficient, even, to power an ATtiny85 at 1 Mhz! The Energizer CR2032 spec sheet isn’t much better, with continuous drain measured at .19mA, though it does allow for 2-second pulses at a whopping 6.8mA.
Something’s off here; the CR2032’s capabilities appear grossly understated. Time for some real-world testing:
Test 1: OLED Screen and ATtiny85
For my first test, I set up an ATtiny85 with the same program running at the end of this article, but with a .96” OLED as shown in the image above. Testing with a 3V power supply, this setup draws 9mA. Subbing in a CR2032 battery, I got the following results over a day or so of testing:
(1).png)
Image Credit: Spreadsheet Screencap
The data shows that the CR2032’s voltage output drops precipitously from its initial not-quite-3V state to less than 2.5V in about a half hour, hovering around that level until the ~2-hour mark. From there it’s a steady drop to 1.5V at 12 hours, settling to just over 1.3V after 24 hours.
Observing its decline, the OLED screen was still (barely) visible after more than 25 hours, but it did not display anything when power from the battery was cycled. Given that the ATtiny85’s minimum voltage requirement (for the -V version) is 1.8V, I suspect it wasn’t submitting new info to the display.
Test 2: LED with 47 Ohm resistor
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Image Credit: Jeremy Cook
For the second test, I hooked up a red LED with a 47-ohm resistor in series, producing a current draw of 18mA with a 3V power supply. This produced the following results with a CR2032 subbed in as the power source:.png)
Image Credit: Spreadsheet Screencap
Interestingly, after a sharp initial drop to just under 2.5V, voltage soon evened out to around the 2V range well beyond 40 hours. I suspect this is due to the LED’s power behavior and that it can quite happily shine at a decreased brightness to compensate for lowered voltages.
In both tests the CR2032 battery sources much more instantaneous current than we might suspect from examining the datasheets.
So, What is Going On?
My suspicion in the case of Energizer and Panasonic CR2032s is that they market and specify these batteries for backup and intermittent use cases, where a minimal amount of current is required over a long period of time. As hardware hackers, we may stretch this beyond how the batteries are marketed.
One might also consider that voltage drops off dramatically at higher current draws. In such cases, calling a CR2032 battery a nominal 3V device becomes unrealistic. Duracell’s datasheet does feature a bit more information, listing a maximum continuous discharge of 6 mA and a maximum 1-second pulse discharge of 20 mA. The service hours rating is comparatively pitiful at 1 kOhm (V/R = I, 3V/1000Ω = 3mA), seen in the chart below. In this case, voltage output drops below 3V almost instantaneously..png)
Image Credit: Duracell datasheet screencap
All that being said, I would try to keep CR2032-powered projects under a 3mA continuous drain if possible. To compensate for longish pulses, one could use a capacitor to help keep the battery discharge even, and/or two CR2032s in parallel could be appropriate in some situations.
CR2032 Power Alternatives
Some time ago (before I considered doing this article) I tried to power a Raspberry Pi Pico project with a CR2032 and/or a pair of them. This setup powered the device for a very short time, on the order of 30 seconds, then stopped working. Since the Pico draws somewhere in the range of 40mA, this out-of-spec current draw kills these 225 mAh cells in short order.
In such cases, you might consider other alternatives, like a small LiPo battery. While this means extra circuitry to control charge/discharge cycles, they can provide a significantly higher constant current than CR2032 batteries. Even better, your board can simply be plugged in for recharging if the electronics are set up correctly. In my previous review of the Bee Data Logger, I experimented with using a 105mAh LiPo to power the device. This has a lower total current capacity than a CR2032 battery, but it can discharge current much faster.
Another alternative would be to use a supercapacitor as a rechargeable energy source or perhaps in conjunction with a CR2032. These devices typically provide a lower total energy capacity than batteries but can discharge a massive amount of current at one time if needed. Supercapacitors also don’t typically need circuitry to prevent over charge/discharge, and they can cycle between charged and discharged states many more times than a LiPo. You could also consider using a solar panel with a supercap setup to allow your device to run indefinitely!
Conclusion
When using battery power, it’s important to consider not just the nominal current output over time in milliamp-hours (mAh), but also the maximum instantaneous current output in milliamps. Also consider if a disposable battery is the right choice, or if a rechargeable device would better suit your needs. In the case of CR2032 batteries, the maximum current discharge is very low, even if you can possibly stretch things further than the datasheets would imply.
