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Home › Batteries › SR421SW
Watch battery

SR421SW battery

1What it is2Safety3Other names4Facts5Buy it
  1. 1

    What it is

    SR421SW+ 1.55V

    SR421SW is a watch battery, about as wide as a pencil eraser. It gives 1.55 volts.

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  2. 2

    Safety first

    Keep away from children and pets

    A swallowed coin or button battery can cause serious burns inside the body within 2 hours. If you think one was swallowed, get emergency help right away.

    Swallowed one? What to do now →
  3. 3

    Names you might see in the store

    All of these are the same battery. Any of them will work.

    SR421348
  4. 4

    Quick facts

    Size
    About as wide as a pencil eraser
    Thickness
    As thick as 3 credit cards stacked
    Power
    1.55 volts
    Keeps in a drawer for
    About 5 years
    Rechargeable?
    No, use once
    Found in things like
    Small ladies’ watchesPrecision instruments
  5. 5

    Where to buy it

    As an Amazon Associate, KnowYourBatteries.com earns from qualifying purchases.

    Amazon searchEnergizer listings, any pack sizeSearch Amazon for Energizer SR421SW
    See results on Amazon →
    Amazon searchMulti-packs from any brandSearch Amazon for SR421SW multi-packs
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    Amazon searchDuracell listings, the same batterySearch Amazon for Duracell SR421SW
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See it at real size

SR421SW next to a US quarter and an AA battery. “Real size” matches your hand once your screen is set up in Measure it.

SR421SWThickness 2.2US quarterAA

What do the letters mean?

Battery names are a code. Here’s how to read SR421SW:

SSilver oxide chemistry (1.55V)
RRound coin / button form factor
4≈ 4 mm diameter (exact 4.8 mm, 0.189 in)
212.1 mm thickness (exact 2.2 mm, 0.085 in)
SWLow-drain variant for analog watches

The same battery from each brand

BrandTheir name for it
Official nameSR421SW
Murata (formerly Sony)348
MaxellSR421SW

Exact measurements

Width
4.8 mm (0.189 in)
Thickness
2.2 mm
Voltage
1.55V (empty at 1.2V)
Energy stored
12 mAh
Weight
—
Made with
Silver oxide
Works between
-10 … 60 °C
Official code
SR421SW

Questions people ask

Is SR421SW the same as SR421?

Yes. They’re the same battery with different names. You might also see SR421, 348.

How long will a spare keep in a drawer?

About 5 years if it stays cool and dry.

Can I recharge it?

No. Never try to recharge it.

Which way up does it go?

Usually with the side marked “+” facing you or facing up. Look at how the old one sits before you take it out.

SR421SW+ 1.55V
SR421SWWatch battery
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1What it is2Safety3Other names4Facts5Buy it