SR521SW battery equivalent

SR521SW is the silver-oxide watch cell Energizer and Renata sell as 379, 5.80 mm across and 2.15 mm tall, rated 1.55 V. Renata’s datasheet title reads SR521SW (SR63). The two makers agree on size and voltage but not on capacity: Energizer’s sheet says 14.5 mAh, Renata’s says 16 mAh.

Why 14.5 and 16 mAh

Both figures are to 1.2 V, but they are measured under different loads: Energizer rates 14.5 mAh on a 68 kΩ continuous drain, Renata rates 16 mAh on 47 kΩ. They are two ratings, not one cell measured twice, so the box below lists both with their sources and does not average them. Renata’s product page shows the height as 2.1 mm; its datasheet gives 2.15 mm, the figure used here.

Energizer’s sheet is marked OBSOLETE

The Energizer 379 datasheet we checked carries the word OBSOLETE across the page. The sheet gives no reason and no replacement, so we can’t say what Energizer sells in its place. Renata still lists its own 379 (OEM) with a datasheet dated 2019/08. The Energizer figures above come from that stamped sheet.

Other brands’ numbers

Renata’s cross-reference for its 379 lists Maxell SR521SW, Panasonic SR521SW, Murata SR521SW, Toshiba SR521SW under the same SR521SW name, plus Energizer Eveready 379 and 6 more. That is Renata’s list; the other brands’ own sheets weren’t checked for it. Energizer’s sheet prints the ANSI / NEDA name 1191SO and no IEC name.

Not a 364 / SR621SW

The 364 has the same 2.15 mm height but is 6.80 mm across, a millimetre wider than the SR521SW:

Specs, with sources

SR521

SR521SW: 379 (silver oxide)

Maker part numbers checked: Energizer 379, Renata 379

Chemistry

Silver oxideEnergizer 379 datasheet, PDF p. 1 · Renata 379 datasheet, PDF p. 1 · checked 2026-10-04

Voltage

1.55 VEnergizer 379 datasheet, PDF p. 1 · Renata 379 datasheet, PDF p. 1 · checked 2026-10-04

Diameter

5.80 mmEnergizer 379 datasheet, PDF p. 1 (upper figure of the range on the drawing) · Renata 379 datasheet, PDF p. 1 · checked 2026-10-04

Height

2.15 mmEnergizer 379 datasheet, PDF p. 1 (upper figure of the range on the drawing) · Renata 379 datasheet, PDF p. 1 · checked 2026-10-04

Rated capacity

Sources disagree

Each maker rates capacity under its own test load and cut-off voltage, so the figures below aren’t measured the same way.

• 14.5 mAh — Energizer 379 datasheet, PDF p. 1 (68 kΩ continuous, to 1.2 V) (checked 2026-10-04)
• 16 mAh — Renata 379 datasheet, PDF p. 1 (47 kΩ, to 1.2 V) (checked 2026-10-04)

Codes printed on the SR521 datasheets

• 1191SO printed on Energizer 379 datasheet“Designation: ANSI/NEDA-1191SO” · checked 2026-10-04
• SR521SW printed on Renata 379 datasheet“379 SR521SW (SR63)” · checked 2026-10-04
• SR63 printed on Renata 379 datasheet“379 SR521SW (SR63)” · checked 2026-10-04

Renata’s cross-reference list

Renata, a battery maker, prints these other brands’ part numbers next to its own on each product page. They are Renata’s cross-references, not those brands’ own statements.

Renata 379: Maxell SR521SW, Panasonic SR521SW, Murata SR521SW, Toshiba SR521SW, Energizer Eveready 379, Varta V379, Rayovac 379, Duracell D 379, Timex JA, Citizen 280-59, Seiko SB-AC/DCRenata 379 product page · checked 2026-10-04

All codes on this page: 1191SO, Citizen 280-59, Duracell D 379, Energizer Eveready 379, Maxell SR521SW, Murata SR521SW, Panasonic SR521SW, Rayovac 379, Seiko SB-AC/DC, SR521SW, SR63, Timex JA, Toshiba SR521SW, Varta V379.

What this page doesn’t cover

Other cells

How values are checked and what “equivalent” means here: method.