The SR626SW, known everywhere as the 377, is probably the most-fitted watch battery in the world. It is a 1.55 volt silver-oxide cell, 6.8 mm in diameter and 2.6 mm tall, holding 25 to 28 mAh, and it runs the majority of small analog quartz watches.
SR626SW, face and side profile, drawn to scale: 6.8 mm across, 2.6 mm thick.
Voltage
1.55 V
Size (D×H)
6.8 × 2.6 mm
Chemistry
Silver oxide (Ag2O)
Capacity
25-28 mAh
Same battery, other names
Every code below is the exact same cell as SR626SW. Any of them will fit and work identically.
377SR66V377D377SR626W (376, high drain)
Compatible replacements
LR626 / AG4: Alkaline same-size cell; a cheap stand-in with about half the watch life.
Buying and replacement notes
The 377 and SR626SW markings appear together on most packaging; they are one battery. Its high-drain twin is the 376 (SR626W), for movements with lights or alarms. Counterfeits of premium brands circulate online in this size, so buy Murata, Renata, Seizaiken or Energizer from reputable sellers. The alkaline AG4 fits the same recess but is a false economy in any watch you plan to keep.
⚠️ 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
Is the 377 battery the same as SR626SW?
Yes. 377 is the industry retail number and SR626SW the IEC code for the identical silver-oxide cell: 1.55 V, 6.8 mm across, 2.6 mm tall. Packs are usually printed with both codes. AG4 and LR626 mark the alkaline version of the same size.
How long does a 377 last in a watch?
Two to four years in a standard analog quartz watch. Movements draw only about a microamp at rest, so the 377's 27 mAh goes a long way. Watches with second hands that jump in four-second steps are signaling a low battery on many quartz calibers.
Can I use a 376 instead of a 377?
Yes, the 376 (SR626W) is the same size with a high-drain electrolyte. In a plain analog watch it works but may self-discharge slightly faster than the low-drain 377. In a watch with a backlight, alarm or chronograph the 376 is actually the better match.
Why did my watch battery die in six months?
Either the cell was old stock or counterfeit, an alkaline AG4 was fitted instead of a true 377, or the movement is drawing excess current from age or moisture. A watchmaker can measure the movement's consumption in seconds to settle it.