Lithium (coin cell) backup battery

[Maximilian Hohmann]

Hello!

Sorry to be nitpicking, but "lithium ion" batteries are rechargeable batteries that were first introduced to the market in 1991 by Sony (although the invention by Nobel price winner John B. Goodenough dates back to 1979).
Therefore there can be no (commercially available) calculator with a Lithium ion battery before 1991.

But I guess that you mean the non-rechargeable lithium based coin cells (mostly lithium manganese oxide). I don't have all the Sharp and Casio calculators in my collection but the Casio PB700 from 1983 already uses a CR-1220 lihium battery for memory backup. And I am very sure that there must be older ones.

Regards
Max