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Silver-oxide watch (SR)

SR1120W battery: equivalents & specs

The SR1120 is a 1.55 volt silver-oxide cell, 11.6 mm across and 2.05 mm tall, holding around 50 mAh. It is sold as the 391 (SR1120W, high drain) and the 381 (SR1120SW, low drain), two numbers for the same case with differently tuned chemistry.

SR1120W battery drawing: 11.6 mm across, 2.05 mm thick SR1120W 1.55V + ⌀ 11.6 mm 2.05 mm
SR1120W, face and side profile, drawn to scale: 11.6 mm across, 2.05 mm thick.
Voltage
1.55 V
Size (D×H)
11.6 × 2.05 mm
Chemistry
Silver oxide (Ag2O)
Capacity
45-55 mAh

Same battery, other names

Every code below is the exact same cell as SR1120W. Any of them will fit and work identically.

391SR55V391SR1120SW (381, low drain)

Compatible replacements

  • LR1120 / AG8: Alkaline same-size cell; short-life substitute for non-critical uses.

Buying and replacement notes

The 391 turns up in watches with backlights and multifunction movements, while the 381 serves plain slim analog calibers. Both fit anywhere the other does. The alkaline AG8 shares the dimensions but suits only toys and disposables. In the 11.6 mm family, confirm height before ordering: the 391 at 2.05 mm sits between the 365 and the 389.

Commonly used in

watches with backlights (391)slim analog watches (381)small instruments

Need a replacement?

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Comparisons

LR1120 vs SR1120

⚠️ Keep away from children. Swallowed button batteries, especially 20 mm lithium coins, cause severe injury within hours. If a child swallows one, call the 24/7 National Battery Ingestion Hotline (US) at 800-498-8666 or poison control at 800-222-1222 immediately. What every parent should know.

Frequently asked questions

Are the 391 and 381 the same battery?
Same size, different drain rating. Both are SR1120 silver-oxide cells, 11.6 x 2.05 mm at 1.55 V. The 391 (W type) handles pulse loads such as backlights; the 381 (SW type) maximizes life in low-drain analog watches. Either fits the other's compartment.
What alkaline battery matches the 391?
The AG8, also marked LR1120, LR55 or 191, has the same 11.6 x 2.05 mm dimensions at 1.5 V. It works in novelty items, but in watches or instruments it lasts roughly half as long and its declining voltage degrades accuracy.
How long should a 381 last in a watch?
Two to three years in a typical slim analog movement. Around 50 mAh is generous for this thickness. If a watch eats 381s faster than that, have its current consumption measured; aging quartz movements can double their draw.

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