Can I use a 397 instead of a 329?

No. Both are 7.9 mm across, but the 397 is 2.6 mm thick and the 329 is 3.1 mm. A thinner cell won't press against the contacts, so the watch won't run reliably.

How long does a 329 battery last?

In a typical analog quartz watch, two to five years. It holds about 36–41 mAh; a running chronograph, a backlight or an alarm drains it faster. Unused cells keep for several years in the pack.

329 battery equivalents

The 329 is a 7.9 × 3.1 mm silver-oxide cell, used in small and mid-size quartz watches. It's sold under several names: SR731SW.

329 (7.9 × 3.1 mm) from the top and the side, to scale with a US dime (17.9 mm).

Equivalents

Sold as	Type	In a watch
SR731SW, 329	Silver oxide, low drain	Best for an ordinary analog quartz watch

Look-alikes that won't fit

These are also 7.9 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 329 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 397 instead of a 329?: No. Both are 7.9 mm across, but the 397 is 2.6 mm thick and the 329 is 3.1 mm. A thinner cell won't press against the contacts, so the watch won't run reliably.
How long does a 329 battery last?: In a typical analog quartz watch, two to five years. It holds about 36–41 mAh; a running chronograph, a backlight or an alarm drains it faster. Unused cells keep for several years in the pack.