AG4, LR626, LR66, 177/376/377, SR626 & SR626SW Equivalents

Button cell batteries are widely used in everyday devices such as watches, calculators, medical equipment, and small electronics. However, they often cause confusion. 

Because the same battery size can be labeled under different codes like AG4, LR626, LR66,177/376/377, SR626, and SR626SW. These codes vary depending on the manufacturer, battery chemistry, and international standards. 

Understanding the equivalents help you choose the right replacement, maintain device performance, and avoid premature power loss. This guide explains the differences, specifications, common applications, and best practices for handling these coin batteries.

Exploring the world of button battery code is like deciphering a secret language. However, once you understand the basic rules behind the naming systems, it becomes much simpler.

The letter codes provide key information about the battery's physical size and its chemical composition.

The Number indicates Physical Size​

The number in a battery code, such as the "626" in LR626 or the 177/ 377, primarily tells you about the battery's physical dimensions.

For the batteries in our list (AG4, LR626, etc.), the numbers 626, 66, and 177 all refer to a battery that is 6.8 mm in diameter and 2.6 mm high. This is a standardized size from international organizations like the International Electrotechnical Commission (IEC).

Different manufacturers might use different numbers (like 376, 377, or 177) based on their own internal naming systems. But they all mean the same size 6.8 x 2.6 mm.

The Letter indicates Chemical Composition​

The letter(s) at the beginning of the code are the most important part. They tell you the battery's chemistry. This directly affects its performance, voltage, and shelf life. The common letters you will see:

L: Alkaline. Batteries like the LR626 are common. This battery is affordable and offers good general performance.

SR: Silver-Oxide. This chemistry, used in batteries like the SR626SW, provides a very stable voltage and is preferred for precision devices. The "W" often indicates the battery is mercury-free.

AG: This is not an official IEC code. It is a brand-specific designation (often from Renata or similar brands) and generally refers to a Silver-Oxide chemistry battery. Functionally, an AG4 is the same to an SR626SW.

Chart 1: Button Cell Battery Equivalents Guide

Summary: While all these batteries share the same physical size (6.8mm x 2.6mm), they are divided into two main chemical types and not always interchangeable:

Always check your device's manual to ensure you use the correct chemistry.

A Practical Guide to Equivalents​

Understanding the size and chemistry rules allows us to create a simple equivalency chart. The most common silver-oxide batteries, such as SR626SW, AG4, 376, 377, and LR66, are all direct equivalents.

They are the same size and have the same chemistry. An alkaline LR626 or LR66 is the same physical size. This means they are physical equivalent. However, they have different chemistry.

This indicates it is not always suitable for devices designed for silver-oxide power. Always check your device's manual to see if it requires a specific chemistry for optimal performance.

Size, Voltage, Capacity and Discharge ​

Although AG4, LR626, LR66, 177, 376, 377, SR626, and SR626SW all refer to the same physical battery size, their chemistry, voltage stability, and lifespan can differ.

The main difference lies between alkaline (LR/AG/177) and silver oxide (SR/376/377) types. Silver oxide batteries generally last longer and provide a steadier voltage. This makes them more reliable for watches and precision devices.

Chart 2: Battery Feature Comparison

Which One Lasts Longer?

When comparing these button cell batteries, silver oxide types (SR626, SR626SW, 376, 377) generally last longer than alkaline (AG4, LR626, LR66, 177).

Because they have a more stable voltage of 1.55 V throughout most of their lifespan. What's more, they have higher capacity and experience lower self-discharge over time.

This makes silver oxide batteries ideal for watches, medical devices, and precision electronics. While alkaline batteries are better suited for low-drain, cost-sensitive devices. These batteries will drain faster and provide less consistent performance.

Size Consistency across Different Battery Models

Despite the variety of labels, AG4, LR626, LR66, 177/376/377, SR626, and SR626SW share the same physical size 6.8 mm in diameter and 2.6 mm in height.

Regardless of chemistry or brand variations, this dimensional consistency ensures that they are interchangeable in devices for that size. Therefore, users can choose between alkaline or silver oxide based on performance needs without worrying about fitting issues.

Button cell batteries like AG4, LR626, LR66, 177/376/377, SR626, and SR626SW are widely used in small electronic devices that require compact, reliable power.

Their small size, consistent voltage, and ease of replacement make button batteries a standard choice for compact portable devices.

 Chart 3: Common Devices and Their Battery Types

Watches

Watches are one of the most common devices powered by button cell batteries because they require compact, long-lasting, and stable energy.

Silver oxide batteries like SR626SW or 377 are widely used since they provide consistent voltage that keeps time accurate.

For example, a Casio analog watch often uses an SR626SW battery to ensure smooth and reliable operation.

Calculators & Toys

Small electronic devices such as calculators and toys often rely on alkaline button cells like AG4 or LR626 because they are inexpensive and easy to replace.

These devices usually don’t need very high or stable power, making alkaline a practical choice. For instance, a basic Casio pocket calculator frequently uses an LR626 battery.

Medical Devices

Medical instruments such as glucometers, digital thermometers, or hearing aids demand reliable and long-lasting power to deliver accurate readings.

Silver oxide batteries like SR626SW or 376 are preferred because they have higher capacity and stable output.

For example, many Accu-Chek glucometers use SR626SW cells to ensure accuracy in blood sugar testing.

Key Fobs & Small Electronics

Car key fobs, remote controls, and small gadgets often use alkaline button cells like AG4 or 177 since they require compact power sources for intermittent use.

While alkaline versions are sufficient, they may need more frequent replacement compared to silver oxide. For example, a Toyota car key fob may run on an AG4 battery.

Laser Pointers

Laser pointers are small handheld devices that produce a focused beam of light, often used in presentations or pet toys.

They require stable voltage and sometimes higher current, which makes silver oxide batteries like 377 or SR626 suitable.

For example, a red laser pointer used in classroom presentations often relies on a 377 battery for steady brightness.

Keep Them in a Cool, Dry Place: Heat is the enemy of batteries. It makes them lose their charge faster. Do not store them in a hot car or next to a stove. A drawer in an air-conditioned room is perfect.

Keep Them in Their Original Package: The package protects the batteries from moisture and from accidentally touching each other. If you take them out, do not let them loose in a drawer with other metal objects like paperclips or keys.

Do Not Let Batteries Touch Each Other: If the positive (+) and negative (-) ends of different batteries touch, it can create a circuit. This can make the batteries get hot, leak, or even cause a fire. If you don't have the package, you can put a piece of tape over each battery's terminals.

Do Not Put Them in the Refrigerator: For modern batteries, refrigeration is not necessary and the moisture inside a fridge can actually be bad for them. Cool room temperature is best.

Button batteries cannot be thrown away in your regular household trash. They contain metals and chemicals that can be harmful to the environment.

More importantly, they are a major safety hazard for small children and animals. If swallowed, they can get stuck and cause serious, life-threatening injuries in just a few hours.

Step-by-Step Guide:

Although button cell batteries may seem complicated, most codes such as AG4, LR626, LR66, 177, 376, 377, SR626, and SR626SW means the same battery size.

They differ only slightly in their chemistry and performance. By knowing the equivalents and choosing the right type, you can keep your devices running smoothly.

Always store batteries correctly, replace them with the proper equivalent, and dispose of them safely. Doing so can protect both your electronics and the environment.

Read More: 

SR626SW 377 Watch Battery Equivalents and Replacement

What are SR621SW Watch Battery Equivalents?

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