If you’ve got a low-power device that uses three-volt CR2032 coin batteries, check exactly where its connectors are before you buy these Duracells to power it.
You might have heard reports that Duracell coin batteries don’t work in some devices. The good news is that they do in fact work in most of the cycling devices I tried, and it’s fairly easy to tell whether or not they’ll work in yours. But first, a bit of background.
Coin batteries are everywhere these days. You find them in car keys, kitchen scales, laser pointers, computer motherboards, calculators, electronic toys, bank card readers, watches, Apple Airtags and probably a load of other applications I haven’t thought of. In cycling, they power tiny blinky lights, computers, electronic shifters, power meters, pressure gauges, heart rate monitors, and cadence and speed sensors, among other things.
But there’s a problem. Because they’re small and shiny, coin batteries are attractive to little kids when they’re at the stage of exploring the world by finding out how everything tastes. They’re easy for an inquisitive toddler to accidentally swallow, with dire consequences. Electricity from the battery reacts with bodily fluids to cause burns in the oesophagus or stomach which can be fatal. This is not a health and safety gone mad, nanny state theoretical problem. Kids have died after ingesting coin batteries.
To deter kids from eating them, Duracell coats coin batteries with Bitrex. As the name suggests this is an extremely bitter-tasting chemical, denatonium benzoate. In fact, it’s the bitterest substance known to man, triggering no fewer than eight of your bitterness taste detectors and inspiring anyone with a working sense of taste to spit out whatever it’s coated with.
Props to Duracell for protecting young ’uns, then (for patenting the process so other battery makers can’t also make their coin batteries less attractive to kids, not so much). However, anything used as a coating on a coin battery can reduce its ability to deliver electricity, and that might cause problems.
Devices like heart rate monitors, power meters and the Apple Airtags many of us use as anti-theft devices don’t draw a lot of power. The low internal resistance of lithium-chemistry coin batteries makes them ideal for these applications as your device can sip a tiny amount of current from them for a long time. But the Bitrex coating on Duracells can stop them supplying enough power.
I first came across this problem in an article by Josh Centers on the TidBits email newsletter, which covers all things related to Apple devices. Josh’s early Airtags needed new batteries, but he found the Duracells he bought just didn’t work.
The problem cropped up in a cycling context when Twitter user Tom Jones aka @FamilyByCycle posted that he’d bought a Duracell CR2032 to power his 4iiii power meter but it didn’t work. He subsequently found that a “cheap Tesco one worked”. Aha! I thought, that’ll be the Bitrex coating then.
To see how widespread the problem is, I bought a couple of Duracell CR2032s and tried them in various devices. I could only replicate the problem with an Apple Airtag. Various lights and on-bike sensors all worked fine, as did a VDO bike computer I had kicking around from the late Iron Age. (Seriously, this thing has a wired sensor; PocketLint reviewed it in 2004. I have no idea why I still have it. [Because you’re a terrible packrat – Ed.]) Several heart rate monitors worked too, including two of Garmin’s despite Garmin also warning about Bitrex-coated Duracells.
What’s going on?
You can see the Bitrex ring close to the edge of the battery
The Bitrex coating on a Duracell coin battery doesn’t cover the whole battery or even all of one side. Instead, as you can see in this image taken with my trusty macro lens, the coating is in a ring on the negative side of the battery. That just happens to be exactly where Apple has put the contacts in an Airtag. The other eight devices I tried all have the negative contact in the middle.
An Apple Airtag connector is positioned near the edge of the battery, just where Duracell has put the Bitrex
I don’t have a 4iiii power meter to test, but videos online showing how to replace the battery show the negative terminals in the middle of the battery compartment, so it’s a bit of a mystery why Tom had a problem. This video even shows a successful replacement with a Duracell CR2032 . It’s just possible I went off down this battery-swapping rabbit hole because one Twitterer was unlucky enough to get a dud battery, but hey ho, I learned stuff and I hope you did too.
The bottom line then is if you’ve got kids and want to deter them from eating your coin batteries, check that the negative connector is in the middle and if it is, go ahead and choose Duracell.