SR626SW / 377
Button Cells · 4 specs
Direct Answer
An SR626SW (also sold as 377) is a 1.55V Silver Oxide button cell measuring approximately 6.8mm in diameter and 2.6mm in thickness. It's one of the most common watch battery sizes, prized for the flat, stable discharge voltage silver oxide chemistry provides over the cell's life.
Source: IEC 60086-2 · Last reviewed Aug 28, 2026
Specs
| Diameter | 6.80 mm |
| Height | 2.60 mm |
| Nominal Operating Voltage | 1.55 V |
| Chemistry | Silver Oxide |
Why Watches Use Silver Oxide
Watch movements need a steady, predictable voltage to keep accurate time, which is exactly what silver oxide chemistry provides: unlike an alkaline cell's gradually sloping discharge curve, a silver oxide cell holds close to its full 1.55V for most of its usable life before dropping off sharply near the end. That flat curve is why the SR626SW and other silver-oxide button cells became the default choice for watches rather than the cheaper alkaline LR626 equivalent, which shares the same physical size but trades that voltage stability -- and some capacity -- for a lower price.
Silver oxide button cells are sold under a range of equivalent designations depending on the manufacturer, including 377 and SR66, all referring to the same physical format.