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Casio F-91W battery: how long it lasts and how to replace it

The F-91W uses a CR2016 cell that Casio rates at about seven years. Here is how to tell it is running low and how to get it replaced safely.

By the F91W team ·

Casio F-91WB-7 Pure White digital watch

One of the best things about the Casio F-91W is how rarely you think about its battery. It runs on a single CR2016 lithium coin cell, which Casio rates at approximately seven years (Casio F91W-1 specifications).

Real-world life depends on use. Every press of the light, every alarm and every hourly chime takes a little energy, so a watch whose light gets used every night will need a cell sooner.

Signs the battery is running low

  • The display looks faint or fades at an angle.
  • The light is dim or flickers when you press it.
  • The alarm or chime sounds weak.
  • The watch resets or shows random segments.

Any of these means it is time for a new CR2016.

A local watch shop can swap an F-91W battery in a few minutes. The advantages:

  • They have the right small screwdriver and won’t strip the four caseback screws.
  • They will check that the rubber gasket under the caseback is seated properly. The gasket is what keeps everyday splashes out.
  • Some modules need a small reset after a battery change, which a technician will do by habit.

Option 2: doing it yourself

If you are comfortable with small screws, the basic process is:

  1. Lay the watch face down on a soft cloth.
  2. Undo the four screws on the stainless caseback and keep them safe.
  3. Lift off the caseback, taking care not to stretch or lose the gasket.
  4. Note how the old cell sits, release it from its clip, and fit a fresh CR2016 the same way.
  5. Seat the gasket evenly, replace the caseback and tighten the screws gently in a cross pattern.
  6. Set the time again. Our time-setting guide has the steps.

If the display shows nonsense after a battery swap, the module may need a reset. A watch shop can do it quickly.

Will a battery change affect water resistance?

It can if the gasket is pinched, dirty or missing. The F-91W is built for everyday splashes, rain and hand-washing, not swimming. After a DIY battery change, be extra careful around water until you are sure the caseback is sealed.

Buying a new F-91W instead?

Every watch we sell ships free across India and is covered by our 7-day replacement if anything arrives damaged or defective.

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