You can probably quite safely wager your retirement fund that they were not made specially for use in Macs. Several companies, which Apple used to list in its Knowledge Base, made such batteries (eg Eveready 523), but it is probably safe to believe that the batteries were designed for another purpose than for Macs. It is also probably safe to believe that the demise of those other uses is the reason why the batteries are now scarce and pricey. Last time I bought one, there was a Chinese-made equivalent that was obligingly labelled with the type numbers of all the brands that it could replace: A21/A133, 523, PX21, EN133A and PC133A.
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