Can I use a 381 instead of a 366?

No. Both are 11.6 mm across, but the 381 is 2.05 mm thick and the 366 is 1.65 mm. A thicker cell won't let the caseback or holder close, so the watch won't run reliably.

How long does a 366 battery last?

In a typical analog quartz watch, two to five years. It holds about 33–40 mAh; a running chronograph, a backlight or an alarm drains it faster. Unused cells keep for several years in the pack.

366 battery equivalents

The 366 is a 11.6 × 1.65 mm silver-oxide cell, used in thin large quartz watches. It's sold under several names: SR1116SW.

366 (11.6 × 1.65 mm) from the top and the side, to scale with a US dime (17.9 mm).

Equivalents

Sold as	Type	In a watch
SR1116SW, 366	Silver oxide, low drain	Best for an ordinary analog quartz watch

Look-alikes that won't fit

These are also 11.6 mm across, so they look right in the pack, but the thickness is different. They aren't substitutes.

Never use a lithium coin cell in its place. Lithium cells run at 3 volts, twice what a silver-oxide watch movement expects.

Getting a 366 changed

Watch shops in our directory list battery changes from $4.99 to $115, with a median of $15, usually done while you wait. A shop has the tools to open a screw-down caseback without marking it, and can replace the gasket and pressure-test a water-resistant watch. 455 shops in the directory list battery replacement. To do it yourself, follow how to change a watch battery.

Find the closest shops to you. Your location stays in your browser.

Questions

Can I use a 381 instead of a 366?: No. Both are 11.6 mm across, but the 381 is 2.05 mm thick and the 366 is 1.65 mm. A thicker cell won't let the caseback or holder close, so the watch won't run reliably.
How long does a 366 battery last?: In a typical analog quartz watch, two to five years. It holds about 33–40 mAh; a running chronograph, a backlight or an alarm drains it faster. Unused cells keep for several years in the pack.