Reference guide · checked 2 September 2026
The final W or SW in a silver-oxide watch-cell designation carries selection information. Dropping it can merge two products that share size and chemistry but are intended for different drain profiles.
Current Murata and Maxell watch-battery material distinguishes SW low-drain types from W higher-drain types. SR626SW/377 and SR626W/376 both measure 6.8 × 2.6 mm and are both silver oxide, yet the guide lists them as separate products.
The same pattern appears at 9.5 × 2.05 mm: SR920SW/371 and SR920W/370. At 9.5 × 2.7 mm, SR927SW/395 and SR927W/399 form another commonly confused pair.
A basic movement and a movement with alarms, illumination or other pulse loads do not necessarily ask the same thing of a cell. A size-only chart cannot capture that distinction. Use the movement or watch maker’s designation when it is available.
Battery Codebook classifies same-size W/SW pairs as conditional substitutes. Physical and chemical gates pass, but the drain-designation gate differs. That is precisely the kind of difference an equivalence reference should expose rather than hide.
SR626SW/377 pairs with SR626W/376 at 6.8 × 2.6 mm. SR920SW/371 pairs with SR920W/370 at 9.5 × 2.05 mm. SR927SW/395 pairs with SR927W/399 at 9.5 × 2.7 mm.
These pairs are useful precisely because three gates—size, voltage and chemistry—match. The remaining drain gate is therefore easy to overlook.
Watch movements vary. Some impose mainly steady low loads; others include alarms, lights or pulses. The suffix is manufacturer selection information, not a quality grade where one option is always “better”.
Battery Codebook does not claim that every W cell can replace its SW partner or vice versa. It labels the relationship conditional and directs the user back to the movement requirement.
Record the maker number and every visible letter. A worn “377” can be resolved to SR626SW from the current guide; a visible “SR626” without its suffix is incomplete for the drain decision.
Do not infer the missing suffix from dimensions, because the W and SW partners deliberately share the same envelope.
Use both the maker number and SR designation when available. Verify the pair in the current selection guide, check that diameter and height match, and retain the W or SW suffix in notes and search. Find the movement requirement rather than assuming that a higher-drain cell is a universal upgrade.
Murata Watch Battery Selection Guide
Checked 2 September 2026. Device requirements remain authoritative.