Most of the numbers on this site are different names for the same physical cell. The IEC code tells you chemistry, size, and often drain rate.
Prefixes
SR— silver oxide, 1.55 V. Best for quartz watches.LR— alkaline, 1.5 V. Toys, lights, cheap electronics.CR— lithium manganese dioxide, 3.0 V. Remotes, boards, digital devices.BR— lithium carbon monofluoride, 3.0 V. Often listed next to CR for low-drain use.
The digits are the size
After the letters, two or three digits are diameter in tenths of a millimeter, and the last two are height. SR626SW is 6.8 × 2.6 mm. CR2032 is 20.0 × 3.2 mm.
SW vs W
SW is low drain (simple analog hands). W is high drain (light, alarm, chrono). Same can, different ability to deliver a pulse. A high-drain or modern multi-drain cell can run a low-drain watch. A low-drain cell in a high-drain watch may reset when you use the light.
Brand number systems
- Energizer, Renata, Rayovac, and often Duracell use three-digit numbers: 364, 377, 395.
- Maxell, Sony, and Panasonic print the IEC name: SR621SW, CR2032.
- Varta prefixes V: V364, V377.
- Duracell often prefixes D or DL: D364, DL2032.
- Seiko uses SB- codes. Citizen uses 280- codes. Timex and Bulova use short letter or number codes.
Do not mix voltages
A lithium coin looks like a big watch cell. It is not. 3.0 V in a 1.55 V movement can destroy it. Same-size alkaline and silver oxide cells are closer, but silver oxide holds voltage and is the watch-safe choice.