The Olivetti Logos 9 Calculator is a rechargeable printing basic calculator. It comes in two versions, a silver and a black version. Internally, the calculator uses three button cell NiCd batteries.
The original battery is about 1″ (2.5cm) in diameter and I suspect smaller batteries can also be used even if they will not allow the calculator to work independently for long.
Unfortunately NiCd batteries of this type are no longer available, but NiMh batteries are, like this Varta CP300.
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