A watch stops working. You open the battery compartment and find a tiny cell labeled SR626SW. But when you search for a replacement, the results include 377, D377, V377, AG4, LR626, and several other codes.
Which one is actually compatible?
This is more than a naming problem. Button cells can share a nominal voltage while having different dimensions, or share dimensions while using different chemistries. A replacement that looks close enough may fail to make contact, provide shorter service life, or simply not fit.
Instead of memorizing a long equivalency table, this guide uses a five-check compatibility workflow that can be applied to SR626SW replacements and other miniature batteries.
Quick answer: What replaces an SR626SW?
For a watch designed to use an SR626SW silver oxide battery, a properly specified 377 silver oxide battery is a common direct replacement. Manufacturer-marked versions such as D377 and V377 are also commonly listed as equivalents.
The important qualifier is silver oxide. AG4/LR626 cells are generally alkaline batteries of approximately the same physical size. They should not automatically be treated as identical replacements merely because they fit the compartment.
Before buying, compare the actual product datasheet or packaging, not just a marketplace title.
Check 1: Decode the battery rather than matching the label alone
Battery codes come from overlapping manufacturer and industry naming systems. The code printed on a battery is often a combination of standardized size and chemistry information plus a brand-specific commercial designation.
| Marking | What it usually means | Replacement decision |
|---|---|---|
| SR626SW | Silver oxide watch cell | Match the watch's specified type |
| 377 | Common commercial designation for SR626SW-size silver oxide cells | Usually the straightforward choice |
| D377 / V377 | Brand-specific 377 designations | Confirm packaging and datasheet |
| SR66 | IEC family designation | Check manufacturer cross-reference |
| AG4 / LR626 | Generally alkaline cells of similar dimensions | Not a chemistry-identical substitute |
| SR621SW | A thinner silver oxide cell | Not a direct dimensional match |
| SR920SW | A wider, differently sized silver oxide cell | Not a direct dimensional match |
If the packaging contains several numbers separated by slashes, do not assume every number has the same meaning in every manufacturer's catalog. Start with the device requirement and verify the offered cell against it.
For a model-by-model reference, the SR626SW battery equivalents and replacement codes page is a useful next step when an unfamiliar marking appears on a product listing.
Check 2: Confirm the mechanical envelope
A small battery holder has limited tolerance for the wrong cell thickness or diameter.
The conventional SR626SW/377 size is approximately:
- Diameter: 6.8 mm
- Height: 2.6 mm
- Nominal voltage: 1.55 V
- Chemistry: Silver oxide
Those dimensions are nominal size identifiers; the precise tolerances should come from the selected manufacturer's drawing.
Consider a tempting near match: SR621SW. It has a similar 6.8 mm diameter, but a height of approximately 2.15 mm rather than 2.6 mm. The difference is less than half a millimeter, yet that can matter in a spring-loaded holder.
A thinner cell may not be held securely. A thicker one may overload the retaining clip. Neither problem can be resolved simply by checking voltage.
If you're deciding between those two markings, consult this SR621SW and SR626SW size comparison before attempting the swap.
Practical rule: Never bend a watch battery contact to accommodate a cell that has not first been verified as the correct size.
Check 3: Compare chemistry and discharge behavior
SR626SW is a silver oxide cell with a nominal voltage of 1.55 V. A typical LR626/AG4 alkaline cell has a nominal voltage of 1.5 V.
That 0.05 V difference is not the whole story. Silver oxide and alkaline cells also tend to have different discharge curves: silver oxide generally maintains a flatter voltage profile over much of its useful life, while alkaline voltage declines more gradually during discharge.
Why does this matter?
A quartz movement may be designed and tested with a particular battery chemistry, load profile, and voltage range. Using a different chemistry can change service life or end-of-life behavior, even when the battery fits.
However, an alkaline battery does not automatically cause every quartz watch to keep incorrect time. Timing behavior depends on the movement design. The safer engineering conclusion is narrower: use the chemistry specified by the device manufacturer.
For watches that call for an SR626SW/377 silver oxide cell, replacing it with the same chemistry minimizes uncertainty.
Check 4: Don't confuse equal voltage with interchangeability
Suppose a shopping result offers an SR920SW as another 1.55 V silver oxide watch battery. That might sound compatible until you examine the dimensions.
| Property | SR626SW | SR920SW |
|---|---|---|
| Nominal voltage | 1.55 V | 1.55 V |
| Chemistry | Silver oxide | Silver oxide |
| Nominal diameter | 6.8 mm | 9.5 mm |
| Nominal height | 2.6 mm | 2.05 mm |
| Common number | 377 | 371 |
| Direct drop-in replacement | No | No |
An SR920SW is significantly wider than an SR626SW. The shared voltage and chemistry do not solve that geometric mismatch.
For anyone comparing look-alike watch battery listings, the SR920SW vs SR626SW dimensional differences are worth checking before ordering.
A useful mindset: A replacement is compatible only when it satisfies all relevant requirements, not merely one specification.
Check 5: Verify the application and current demand
Two devices using the same size battery do not necessarily consume current in the same way.
For example, a basic analog quartz watch may have a very different current profile from a small electronic accessory with occasional bursts of activity. Some battery variants are marketed for low-drain or multi-drain usage.
When a service manual identifies a particular battery type, follow that specification. If the device uses a specialized movement, its documentation is more authoritative than a generic online compatibility list.
Why capacity numbers vary
You may see listings claiming that a 377 battery offers 24 mAh, 27 mAh, or another nearby capacity.
That is not necessarily a contradiction. Battery capacity is measured under defined testing conditions, including load, temperature, and cutoff voltage. Energizer has published 377/376 datasheets with different typical capacities under different test conditions and product versions.
This means a battery's mAh figure should not be treated as a standalone prediction of how many months a watch will run.
A simplified calculation is:
Ideal runtime (hours) = Rated capacity (mAh) / Average current (mA)
This is only a first-pass estimate. Actual life depends on the voltage threshold of the circuit, intermittent loads, storage age, temperature, and the applicable discharge curve.
A replacement decision workflow
Use this checklist before purchasing or installing a cell:
Read the device or movement specification
|
v
Is SR626SW / 377 silver oxide required?
| Yes | Unknown
v v
Check replacement label Find the movement manual
|
v
Verify diameter and height
|
v
Verify chemistry and voltage
|
v
Check manufacturer cross-reference
|
v
Install only if every requirement matches
This approach is especially useful when online product titles contain long lists of battery numbers. Those lists can be search keywords rather than a guarantee of direct compatibility.
The watch still won't run: A small diagnostic table
| Symptom | What to check first | What not to assume |
|---|---|---|
| No movement after replacement | Cell polarity, exact battery type, contacts | That the new battery is necessarily defective |
| Runs only when pressed or moved | Battery fit and retention | That increasing contact pressure is safe |
| Stops soon after installation | Battery age, movement current consumption | That nominal voltage proves full remaining capacity |
| Case back will not close | Battery height, gasket placement | That extra force is acceptable |
| Timing remains inaccurate | Movement condition and correct cell specification | That a battery swap fixes every timing problem |
If the watch still fails after a verified battery replacement, a qualified repairer can check movement current consumption, contact integrity, and any manufacturer-specific reset requirement.
Do not randomly short electronic contacts in an attempt to reset a movement. Procedures differ between calibers.
Handling and installation precautions
Button cells are easy to short-circuit accidentally with metal tools. Keep the replacement in its packaging until needed, observe the polarity markings, and use appropriate non-shorting tools and techniques.
Also keep the following in mind:
- A water-resistant watch may need a gasket inspection and pressure test after opening.
- If there is visible leakage or corrosion, do not scrape aggressively at the movement or improvise a cleaning process.
- SR626SW cells are not rechargeable.
- Loose button batteries must be kept out of reach of children and pets. Suspected ingestion requires immediate emergency medical attention.
- Dispose of used batteries through an appropriate local collection or recycling route.
For expensive, sealed, or unfamiliar watches, professional battery replacement is often the safer option.
FAQ
Is a 377 battery the same as SR626SW?
A correctly specified 377 silver oxide battery is a common replacement for SR626SW. Confirm the product details, especially when buying from unfamiliar sellers.
Can I use AG4 instead of SR626SW?
AG4 is generally an alkaline type with a similar nominal size, but it is not a chemistry-identical match. Prefer the silver oxide battery specified by the watch maker.
Does the SR626SW battery have to be a particular brand?
Usually the key requirement is the correct specification, not one particular brand name. Choose a traceable product from a reliable manufacturer or distributor.
Is SR621SW close enough?
Its diameter is similar, but its height is different. Do not treat it as a direct drop-in replacement without explicit device-manufacturer approval.
Why did my watch stop immediately after the replacement?
Possible explanations include incorrect polarity, a contact issue, the wrong cell, a low-charge replacement, or a movement fault. A model-specific reset may also be required.
Final takeaway
The easiest way to avoid an SR626SW replacement mistake is to stop treating equivalent battery numbers as a guessing game.
Start with the movement's specified cell. Check the size, chemistry, voltage, and operating requirements. Only then use a cross-reference to select a commercially available replacement.
For most watches that specify SR626SW, a properly matched 377 silver oxide cell is the sensible starting point. An AG4, SR621SW, or SR920SW may appear in the same search results, but similarity in naming or voltage does not establish interchangeability.
A two-minute specification check is far easier than troubleshooting an incorrectly fitted battery.
Technical reference: Energizer 377/376 silver oxide battery datasheet. Specifications are product- and test-condition-dependent; always consult the datasheet of the exact battery being installed.
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