Low Drain vs High Drain Watch Batteries (SW vs W)

Pairs like 377 / 376, 371 / 370, and 395 / 399 share a can. The difference is how hard they can pulse.

SW / low drain — analog time and date. Example: 377, SR626SW.
W / high drain — backlight, beep, chrono, digital module. Example: 376, SR626W.

High-drain in a simple watch is safe. Low-drain in a feature-heavy watch may keep time and then fail when the light fires. Many current Renata, Energizer, and Duracell cells are multi-drain and cover both. If the package only lists one number, it is usually that modern type.

Low drain vs high drain