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I was given an HP-21 and the previous owner had replaced the batteries with standard 1.5 volt batteries. Does anyone know if this may have damaged it and can you tell me which pin is +ve and -ve.


according to the archives that does no harm (if you have any doubt then use used batteries) . the pin on the same side as the enter key is pos.

Thank you

If you have a battery holder that has been opened up, the battery polarity is molded inside the holder.