Is LR521 the same as SR521SW?

Same size, different chemistry. LR521 (also sold as AG0) is alkaline and SR521SW is silver oxide. The alkaline cell fits, but it holds about 8–10 mAh against 13–16 mAh and its voltage drops as it drains, so a watch runs a shorter time on it.

Can I use a 317 instead of a 379?

No. Both are 5.8 mm across, but the 317 is 1.65 mm thick and the 379 is 2.1 mm. A thinner cell won't press against the contacts, so the watch won't run reliably.

How long does a 379 battery last?

In a typical analog quartz watch, two to five years. It holds about 13–16 mAh; a running chronograph, a backlight or an alarm drains it faster. Unused cells keep for several years in the pack.

379 battery equivalents

The 379 is a 5.8 × 2.1 mm silver-oxide cell, used in small quartz watches, including many women's and dress watches. It's sold under several names: SR521SW, LR521, AG0, LR63, SR63.

379 (5.8 × 2.1 mm) from the top and the side, to scale with a US dime (17.9 mm).

Equivalents

Sold as	Type	In a watch
SR521SW, 379	Silver oxide, low drain	Best for an ordinary analog quartz watch
LR521, AG0, LR63	Alkaline, 1.5 V	Fits, but runs down sooner and the voltage sags; use only in a pinch
SR63	Older or alternative codes	Same size; check the chemistry on the pack

Look-alikes that won't fit

These are also 5.8 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 379 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

Is LR521 the same as SR521SW?: Same size, different chemistry. LR521 (also sold as AG0) is alkaline and SR521SW is silver oxide. The alkaline cell fits, but it holds about 8–10 mAh against 13–16 mAh and its voltage drops as it drains, so a watch runs a shorter time on it.
Can I use a 317 instead of a 379?: No. Both are 5.8 mm across, but the 317 is 1.65 mm thick and the 379 is 2.1 mm. A thinner cell won't press against the contacts, so the watch won't run reliably.
How long does a 379 battery last?: In a typical analog quartz watch, two to five years. It holds about 13–16 mAh; a running chronograph, a backlight or an alarm drains it faster. Unused cells keep for several years in the pack.