Comparison

LR621 vs SR621SW

Same thin size (≈6.8 × 2.15 mm) but different chemistry — LR621 is alkaline; SR621SW is silver oxide (often sold as 364). Not automatic equivalents.

At a glance

Question	Answer
Same battery?	No — see chemistry and size below
Same dimensions?	Yes
Same chemistry?	No — do not swap by size alone
Same voltage?	Check each code
Direct substitute?	Only if the device documentation names that exact code

Both are about 6.8 × 2.15 mm — thinner than the LR626 / SR626SW pair. LR621 (also AG1 / LR60) is alkaline (~1.5 V).

SR621SW is silver oxide (~1.55 V), commonly sold as 364. Thin quartz watches that name 364 / SR621SW want silver oxide, not alkaline AG1.

Casio EF-305 and multiple Seiko calibers (e.g. 6N01 / SUR609 family) on this site use SR621SW — not LR621.

Do not treat 364 / SR621SW as an LR621 / AG1 equivalent without checking the device.

Do not confuse this thin pair with taller LR626 / SR626SW (≈2.6 mm) cells.

Label	Resolves to	Type	Size
LR621	LR621	1.5V alkaline button cell	6.8 × 2.15 mm
SR621SW	SR621SW	1.55V silver oxide button cell	6.8 × 2.15 mm

Device counts: LR621 (2) · SR621SW (24)

Same battery, pack labels, or same size with a different type — not a generic “compatible with” list.

From LR621

Same size, different type

Fits the same slot. Different type — check the manual.

From SR621SW

Same size, different type

Fits the same slot. Different type — check the manual.

Shop the code your device names — not a size twin.

Search Amazon for packs of this battery code.

Buy links go to Amazon (Associates where tagged) or other affiliate programmes when available. They never change the battery answer.

Search Amazon for packs of this battery code.

Buy links go to Amazon (Associates where tagged) or other affiliate programmes when available. They never change the battery answer.