CellChart
Button alkaline (LR / AG)

LR521 battery: equivalents & specs

The LR521 is one of the smallest common button cells: 1.5 volt alkaline, 5.8 mm across and 2.1 mm tall. It is also labeled AG0 or LR63. Almost every device this size is a small watch, where the silver-oxide SR521SW, sold as the 379, is the standard fit.

LR521 battery drawing: 5.8 mm across, 2.1 mm thick LR521 1.5V + ⌀ 5.8 mm 2.1 mm
LR521, face and side profile, drawn to scale: 5.8 mm across, 2.1 mm thick.
Voltage
1.5 V
Size (D×H)
5.8 × 2.1 mm
Chemistry
Alkaline (Zn/MnO2)
Capacity
10-13 mAh

Same battery, other names

Every code below is the exact same cell as LR521. Any of them will fit and work identically.

AG0LR63L521379A

Compatible replacements

  • SR521SW / 379: Silver-oxide version, the standard cell for very small ladies' watches.

Buying and replacement notes

At this size the alkaline version is mostly a curiosity found in bargain multi-packs. Watchmakers fit the 379 exclusively, and with good reason: with barely 10 to 16 mAh available, the flat discharge and lower self-discharge of silver oxide make a real difference. If a jeweler quotes you a 379, an AG0 will physically fit but will not serve the watch as well.

Commonly used in

very small ladies' watchesminiature electronics

Need a replacement?

Shop LR521 batteries on Amazon →

⚠️ Keep away from children. Swallowed button batteries, especially 20 mm lithium coins, cause severe injury within hours. If a child swallows one, call the 24/7 National Battery Ingestion Hotline (US) at 800-498-8666 or poison control at 800-222-1222 immediately. What every parent should know.

Frequently asked questions

What is the equivalent of an AG0 battery?
AG0, LR521, LR63 and L521 are the same 1.5 V alkaline cell at 5.8 x 2.1 mm. The silver-oxide equivalent is the SR521SW, universally sold as the 379. It is the standard replacement for small watches that take this size.
Can I use a 379 in place of an LR521?
Yes. The 379 matches the LR521's dimensions exactly and is the better cell: 1.55 V held flat through its life and around 16 mAh of capacity. Any device that accepts an AG0 or LR521 will run correctly, and longer, on a 379.
Why does my tiny watch battery die so fast?
Cells this small carry very little energy, so an alkaline AG0 may only last months. Fit a silver-oxide 379 and make sure the watch is not running a light or alarm feature that this size cannot support well. Two to three years is normal for a 379 in a simple movement.

More Button alkaline (LR / AG) cells

LR44LR43LR1130LR41LR626LR621LR726LR721LR754LR920