CellChart
Silver-oxide watch (SR)

SR621SW battery: equivalents & specs

The SR621SW is the 364, one of the two or three best-selling watch batteries on earth. It is a 1.55 volt silver-oxide cell, 6.8 mm across and 2.1 mm tall, rated around 20 mAh, and it powers millions of small analog quartz watches.

SR621SW battery drawing: 6.8 mm across, 2.1 mm thick SR621SW 1.55V + ⌀ 6.8 mm 2.1 mm
SR621SW, face and side profile, drawn to scale: 6.8 mm across, 2.1 mm thick.
Voltage
1.55 V
Size (D×H)
6.8 × 2.1 mm
Chemistry
Silver oxide (Ag2O)
Capacity
18-23 mAh

Same battery, other names

Every code below is the exact same cell as SR621SW. Any of them will fit and work identically.

364SR60V364D364SR621W (363, high drain)

Compatible replacements

  • LR621 / AG1: Alkaline same-size cell; fits but with roughly half the useful life in a watch.

Buying and replacement notes

If a watch shop pulls a battery out of a small ladies' or midsize watch, odds are good it is a 364. The high-drain variant, SR621W or 363, shares the same case and serves movements with heavier pulse loads; for a plain two- or three-hand watch the standard 364 is correct. The alkaline AG1 fits too but roughly halves the service life.

Commonly used in

ladies' watchessmall analog watcheswatch movements (mini calibers)

Need a replacement?

Shop SR621SW batteries on Amazon →

Comparisons

LR621 vs SR621SW

⚠️ 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

What battery is equivalent to the 364?
The 364 is the SR621SW; every brand's version at 6.8 x 2.1 mm is the same cell. The 363 (SR621W) is its high-drain sibling in the identical case, and the alkaline AG1/LR621 fits the same slot with shorter life and looser voltage.
364 versus 363: which do I need?
The SW-type 364 is designed for low-drain analog watches, which is nearly every simple quartz watch. The W-type 363 handles high pulse currents in watches with alarms, lights or chronograph motors. Both fit; matching drain type maximizes battery life.
How long does a 364 last?
Two to three years in a typical small analog watch is normal, sometimes longer in efficient modern movements. Because silver oxide holds 1.55 V until nearly empty, the watch keeps accurate time throughout and stops quite suddenly when the cell is done.

More Silver-oxide watch (SR) cells

SR416SWSR512SWSR516SWSR521SWSR527SWSR616SWSR626SWSR716SWSR721SWSR726SW