There are a lot of button batteries out there with the same diameter
and voltage, and which differ only in the thickness of the battery. If
you buy a card of them, there'll often be 2 each of 4 sizes.

I invariably only want one size, and the others are completely surplus
to requirements, which seems a waste.

The difference in thickness is sometimes minor, so is there any
particular/dangerous reason why I can't use one of the others (assuming
it fits in the battery compartment without forcing anything)?

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Cheers, Harvey