The battery code is printed on the old battery itself. If it’s gone, Swatch, and Timex’s W33 guide, say it’s on the back of the case, and Citizen lists it by the caliber number engraved there.
Which brand?
The battery and who changes it
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Common watch batteries
Silver oxide watch cells have an SR code and a short number such as 377. Watch makers give the same cell their own codes too.
| SR code | Number | Size (mm) | Watch makers’ codes |
|---|---|---|---|
| SR626SW | 377 | 6.8 x 2.6 | Citizen 280-39, Seiko SB-AW, Timex BA |
| SR621SW | 364 | 6.8 x 2.1 | Citizen 280-34, Seiko SB-AG/DG, Timex T |
| SR927SW | 395 | 9.5 x 2.7 | Citizen 280-48, Seiko SB-AP/DP, Timex LA |
| SR927W | 399 | 9.5 x 2.7 | Citizen 280-44, Seiko SB-BP/EP, Timex W |
| SR920SW | 371 | 9.5 x 2 | Citizen 280-31, Seiko SB-AN |
| SR936SW | 394 | 9.5 x 3.6 | Citizen 280-17, Seiko SB-A4 |
| SR916SW | 373 | 9.5 x 1.6 | Citizen 280-45, Seiko SB-AJ/DJ, Timex WA |
| SR616SW | 321 | 6.8 x 1.6 | Citizen 280-73, Seiko SB-AF/DF, Timex DA |
| SR521SW | 379 | 5.8 x 2.1 | Citizen 280-59, Seiko SB-AC/DC, Timex JA |
Size is diameter x height. A code ending in SW and one ending in W can share a size, such as SR927SW (395) and SR927W (399).
Finding the code
- Read the code on the old battery, if it’s still in the watch or you kept it.
- Look on the back of the case for the battery type or the caliber number.
- Look the model or caliber up in the maker’s own list, such as Timex’s manuals page or Citizen’s battery list.
Solar and rechargeable watches
Citizen’s list marks cells such as the MT621S, MT920S and CTL920F as rechargeable, and they make up most of its rows.
Keep button batteries away from children
The National Capital Poison Center says that if anyone swallows a battery, immediately call the 24-hour National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222. Don’t delay. Immediate treatment decreases severity.