The Bitter Truth About Coin Cells

December 5, 2021

Only a couple of weeks ago I wrote about the ubiquitous 2032 battery and, along with 9 volt batteries for our home smoke detectors, and AA and AAA batteries, why it’s just handy to have these around. It’s annoying when a device stops working and there is no quick fix, and for us that could mean heart rate monitors, electronic shifters, power meters and more.

I was very satisfied with the story I wrote except for an inaccuracy – I originally reported that the PowerTap pedal used this battery when in fact it didn’t – and the fact that I chose the one battery installed in the one device that together represent the one incompatibility of devices and this battery. This is of course why most of these articles are best left to either the esteemed DC Rainmaker, or to our own Brian Gray. That said… I was left with this outstanding question and I felt I needed to get to the bottom of it, so I asked my friends at Quarq and what they reported is as follows.

The affected problem, that caused cadence dropouts and other signal losses, was the particular starfish-shaped battery contact (pictured above). It interfaces with the bitter taste area on the 2032 battery that Duracell makes, which is near the perimeter of the battery. That bitter taste, as you know, is designed to discourage the placement of the battery into one’s mouth, which is a habit common to children in particular (and, one might assume, pets). This is a Duracell feature.

Since SRAM owns Quarq I took the opportunity to ask about the SRAM shifters, which use this same battery. The contact in the shifter (e.g., the SRAM AXS road shifters or the Eagle shifters) is of a different design, the contact not on the perimeter of the battery.

I likewise looked at the battery contact on a Wahoo TICKR heart rate monitor (you’ll see what the contact looks like in the pic above), and on a Stages power meter (which I have on the Stages SB20 Smart Bike in my studio). In each case, as you see, the contact occurs on or near the center of the battery, not near the perimeter. The Stages contact is below.

While the TICKR’s contact area hits the center of the battery, Wahoo Fitness did onboard a few customer service tickets when Duracell bitter coating batteries first entered the market. Accordingly, Wahoo Fitness did put a small disclaimer on our support site, recommending that its customers not use them. Then Duracell saw that disclaimer and reached out to Wahoo, and Wahoo shared some engineering drawings and product specs. Wahoo then tested that Duracell battery in its TICKER again, in-house, and found that there is no reason that the bitterant coating should interfere with TICKR performance. Accordingly, Wahoo removed the disclaimer from its site. Just know that all TICKRs come with Panasonic batteries installed from the factory, which present no problem.

As for SRAM and Quarq, starting February upcoming (2022) all spider-based power meters will ship with its new battery contact that is bitter coating friendly. This new contact will be backward-compatible with all spider-based power meters manufactured since 2012, which means that if owners want to change out the original equipment spider contact with the new bitter-coating-friendly one, that can be done.

The upshot is that both Duracell and the sporting world is aware of the issue; Wahoo appears to (at least guardedly) stipulate to the usability of the battery with the bitter coating (assuming such coating is applied on the battery’s perimeter, as Duracell’s is); SRAM’s shifters (eTap AXS and Eagle) use a center battery contact patch; I’m running Duracell bitter coating on my Stages power meters so-far without incident (the Duracell battery in the Stages PM is pictured just above); and SRAM and Quarq are replacing the starfish-shaped contacts in 2 months of this writing so that they will be unfriendly-taste-friendly.