Smooth, shiny coin batteries never fail to catch the eye of small children, but they can result in a trip to the emergency room and serious complications if swallowed. So Duracell is taking action by making its coin batteries taste horrible.
Citing the NBIH Biennial Report (Jul 2014 – Jun 2016), Duracell says, "Every year hundreds of lithium coin batteries are accidentally ingested, with more than half being swallowed by children under age 6." Ingesting the batteries causes a harmful chemical reaction in the body within a couple of hours, so discouraging kids putting them in their mouths is highly desirable.
As The Verge reports, Duracell is adding a bitter coating to the back side of its 2016, 2025, and 2032 lithium coin batteries, with the company explaining that, "If a child puts a lithium coin battery in their mouth, the bitter coating will immediately react with saliva to release a bitter taste which will discourage swallowing." Other measures in place to stop children digesting these tiny batteries include packaging that's "child-secure," although many would argue it's adult-secure, too. Duracell also includes on-pack safety warnings and there's an engraved warning on the positive side of the battery, so it's very clear they need to be kept away from kids.
If a bitter coating being added to small objects sounds familiar, it's probably because Nintendo did the same thing for Switch cartridges. The coating used on the carts is denatonium benzoate, which is a non-toxic chemical compound used to help prevent nail biting. It's likely Duracell is using the same compound, or something similar for its batteries.