Casio · Watches

Casio F-91W battery

1 × 3V lithium coin cell

Printed IDs: 593 (Module)

How to replace it

Notes	Case-back service typically required; water resistance should be retested after opening. This model uses a screw-secured caseback — not a Jaxa-style snap/screw-ring opener.
Access	Professional recommended

Last checked 7 October 2026

Casio F-91W uses 1 × CR2016.

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Optional tools for opening, testing or charging — separate from the battery answer.

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Fluke 101 Digital Multimeter
Accurate open-circuit voltage and basic electrical checks
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Klein Tools MM400 Multimeter
General DC voltage checks including battery terminals
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Digital multimeter
Measure open-circuit voltage and general electronics checks
Voltage alone does not establish usable capacity, especially for rechargeables.
Tester vs multimeter Buy on Amazon

Buy links are optional and separate from the battery answer.

Casio F-91W is still sold new. Only buy another if a fresh battery and the checks above did not help.

Buy links go to Amazon (Associates where tagged) or other affiliate programmes when available. They never change the battery answer.