SR621SW Battery: A Compact Powerhouse for Watches

When it comes to watch batteries, few models are as commonly used and frequently searched as the SR621SW. Known for its small size and consistent performance, this silver oxide button cell is widely compatible with various watch brands like Seiko, Accurist, Fossil, and more. But many users are still puzzled by questions like "What is the equivalent of an SR621SW?", "Can I use a SR626SW instead?", or "What's the difference between SR621SW and 364?"
In this guide, we'll break down all you need to know about the SR621SW watch battery, including equivalents, replacements, and trusted brands like Sony, Maxell, Renata, and Duracell.

What is SR621SW?

The SR621SW is a 1.55V silver oxide button battery, also labeled as 364 in many brand catalogs. It's typically used in analog wristwatches, medical instruments, and small electronics. The number 621 indicates its size-6.8mm in diameter and 2.1mm in height, making it compact enough for thin watch casings.

Common Uses:

Watches (SR621SW watch battery)
Small medical devices like thermometers
Calculators and toys

SR621SW Battery Equivalents: What Can You Use Instead?

Looking for an SR621SW battery equivalent? You'll often find this battery cross-listed as:

1. 364 (Maxell 364 SR621SW, Renata 364 SR621SW)
2. 377 (SR621SW equivalent 377 in some low-drain uses)
3. SR621 (without the "SW", just a naming variant)
4. LR621 (alkaline version, lower capacity)

Some users also ask: "Can I use SR626SW instead of SR621SW?" Technically, SR626SW is slightly taller (2.6mm vs. 2.1mm), which can cause fitting issues in some tight battery compartments. So while SR626SW vs SR621SW might seem similar, they're not perfect substitutes unless your device allows some flexibility.

Replacement Options and Compatibility

When searching for SR621SW battery replacement, check these well-known options:

1. Sony SR621SW HG 0 – mercury-free and long-lasting
2. Maxell SR621SW – equivalent to 364
3. Renata 364 SR621SW – trusted Swiss quality
4. Energizer 364 – reliable and widely available
5. Duracell SR621SW – another solid silver oxide performer
6. Seizaiken SR621SW – Seiko's OEM battery

If you're buying online, you'll often see listings like "SR621SW Battery Amazon" or "SR621SW Battery Walmart" – just make sure it's silver oxide (not alkaline), and from a reputable brand.

Understanding Battery Codes: SR621SW vs LR621 vs 364 vs 377

Many buyers get confused with similar codes. Here's a breakdown:

Battery	Chemistry	Voltage	Height	Equivalent to SR621SW?
SR621SW	Silver Oxide	1.55V	2.1mm	✔ Yes
LR621	Alkaline	1.5V	2.1mm	✖ Not recommended
SR626SW	Silver Oxide	1.55V	2.6mm	✖ May not fit properly
364 Silver	Oxide	1.55V	2.1mm	✔ Exact equivalent
377 Silver	Oxide	1.55V	2.6mm	✖ Only if compatible

So when comparing SR621SW vs 364, they're basically the same. But for SR621SW vs 377 or SR621SW vs SR626SW, always check your device manual.

Popular Watch Brands Using SR621SW

If you own any of the following watches, there's a good chance they're powered by the SR621SW battery:
Accurist SR621SW Watch
Seiko watches (Seiko SR621SW)
Fossil Watch Battery SR621SW
Citizen, Casio, Swatch, Timex
Make sure you check the back case of your watch or consult the manual before choosing a replacement.

Pila SR621SW: Spanish Users' Note

In many Spanish-speaking regions, you'll see the battery listed as:
Pila para reloj SR621SW
Pila SR621SW equivalencias
Pila SR621SW Seiko
These are direct references to the same battery. Use "equivalente de pila SR621SW" to find local replacements or equivalents like 364 Renata or Maxell SR621SW equivalente Energizer.

Conclusion: Know Before You Replace

The SR621SW is a dependable, long-life battery perfect for watches and small electronics. Understanding its equivalents like 364, 377, and potential substitutions helps ensure you always get the right fit and performance. Whether you're replacing a Fossil, Seiko, or Accurist SR621SW watch battery, choosing a silver oxide variant from trusted brands like Sony, Renata, or Maxell is your best bet.
Still unsure which one to buy? Stick to 364 Renata SR621SW – it's widely compatible and reliable.