This post on the University Of Vermont Medical Center's website about button cell battery ingestion is interesting:
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medcenterblog.uvmhealth.org
The bottom line, IMHO, is that these things certainly CAN be dangerous for kids and pets ... and if it's going to be accessible to them, adults are responsible to make sure it is in some sort of a child/pet-proof case.
It would be absurd to say that everything in the world must be child-safe ... Parents have a responsibility ... but certainly it's worth at least pointing the danger out so that people who haven't thought of the danger are aware of it.