Batteries / SR
SR521
Silver oxide / zinc
Cross-checked Primary batteryReviewed:
Reference dimensions are not universal manufacturing tolerances. Check the actual cell and holder.
The type status describes documentary checks of core specifications, not every fact or suitability for a device.
Understanding SR521 before replacement
Identify the actual battery
SR521 is a documented Silver oxide / zinc primary cell with a nominal voltage of 1.55 V. Its reference diameter is 5.8 mm and its reference height is 2.15 mm. These are nominal reference dimensions, not a promise that every manufacturer has identical tolerances.
This dataset describes a non-rechargeable bare cell, without solder tabs or wires. A tabbed or wired assembly requires a separate fit check.
What markings identify this type?
The dataset associates SR521SW, SR63, 379 with SR521. The manufacturer may use a different label on the package. These references help identify the type; they do not certify the battery for a particular device.
A suffix such as W or SW describes a discharge/load variant. Preserve this requirement when choosing a replacement.
Similar dimensions in this catalogue
The following types share the same reference diameter as SR521. Their height, chemistry or voltage may differ. They are comparisons, not approved substitutes:
What to check before replacing SR521
Read the original device marking, verify nominal voltage and chemistry, compare diameter and height, and check the contacts and load requirements. Same diameter, identical voltage, or a familiar brand prefix alone is not enough to establish interchangeability.
The available data contains no affirmative device-specific fit test for SR521. A missing compatibility relation means “not assessed,” not “compatible.”
How reliable are these specifications?
Core type characteristics were compared with primary material from at least two independent publishers. This does not verify all model-specific values or physical suitability.
Technical specifications
| Designation | SR521 Cross-checked using documents from two independent publishers [Seiko Instruments] [Maxell] |
|---|---|
| Chemistry | Silver oxide / zinc Cross-checked using documents from two independent publishers [Seiko Instruments] [Maxell] [VARTA Consumer Batteries] |
| Nominal voltage | 1.55 V (Nominal) Cross-checked using documents from two independent publishers [Seiko Instruments] [Maxell] [VARTA Consumer Batteries] |
| Diameter | 5.8 mm Cross-checked using documents from two independent publishers [Seiko Instruments] [Maxell] [VARTA Consumer Batteries] |
| Height | 2.15 mm Cross-checked using documents from two independent publishers [Seiko Instruments] [Maxell] |
| Rechargeable | No Documented source [Seiko Instruments] |
| Terminal form | Bare cell without tabs or leads Documented source [Seiko Instruments] |
Reference dimensions are not universal manufacturing tolerances. Check the actual cell and holder.
Other designations
These codes identify the same type family. Match the load variant, terminals and device requirements separately.
SR521SWSW / low drain [Seiko Instruments]SR63[VARTA Consumer Batteries]379SW / low drain [Seiko Instruments Inc.]
W and SW are different load variants. The combined 357/303 product does not make every 357 and 303 product interchangeable.
Documented brands
Brand presence comes from product documents or documented code mappings; current availability is not checked.
Product-specific observations
Capacity belongs to an individual product and test regime. It is not a universal value for this battery type.
Seiko Instruments SR521SWDocumented source
Current availability not checked · SW / low drain [Seiko Instruments]
Documented product; no individual technical observations in this dataset.
Replacement limits
Device compatibility has not been verified. Dimensions alone do not prove that a battery fits or works.
Replacement evidence by category
Other markings of this technical type
SR521SW SW / low drain · SR63 · 379 SW / low drain
These markings resolve to this type in documented sources. The exact variant and device requirements still matter.
Conditional replacement: review requirements
No conditional cross-type relation is recorded.
Known obstacles to direct replacement
No explicit obstacle is recorded here; that is not evidence of compatibility.
Other type pairs without a recorded assessment
This pair has not been assessed. No compatibility conclusion is available.
No automatic replacement recommendation. Device compatibility has not been verified. Dimensions alone do not prove that a battery fits or works.
Sources & verification
- Seiko Instruments · v021-seiko Documented source
SEIZAIKEN mercury-free silver oxide batteries — manufacturer dimensions and nominal voltage
Current availability not checked
· Reviewed: - Maxell · v021-maxell Documented source
Silver Oxide Batteries SR / Alkaline Button Batteries LR — manufacturer specifications
Current availability not checked
· Reviewed: - VARTA Consumer Batteries · v021-varta Documented source
VARTA Gesamtkatalog 2024/25, Silver Coin cross-reference, PDF p. 145
Current availability not checked
2024/25 · Reviewed: - Seiko Instruments Inc. · v0210-src-sii-silver-crossref Documented source
Silver Oxide Battery CROSS-REFERENCE CHART (Watch Battery Low-Drain / High-Drain)
Current availability not checked
· Reviewed:
Common questions
What size is SR521?
Ø 5.8 × 2.15 mm
Can SR521 be recharged?
No. Do not charge primary cells.
Can SR521 replace another battery?
Not on the basis of size or matching names alone. Check the exact device requirements and the directed compatibility notes. This catalogue does not contain a guaranteed device-fit recommendation for SR521.
How does SR521 differ from SR516?
SR521 and SR516 have reference heights of 2.15 mm and 1.65 mm respectively, and nominal voltages of 1.55 V and 1.55 V. Their chemical systems are Silver oxide / zinc and Silver oxide / zinc. These comparisons do not establish a permitted replacement.
Open technical comparison: SR516
This is a technical comparison, not an equivalence or fit certificate.