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Understanding Watch Battery Types and Their Sizes

Watch batteries come in many different sizes and types, and knowing which one your watch needs is the first step to replacing it yourself. Unlike car batteries or phone batteries, watch batteries are small and use a standardized numbering system that tells you their exact dimensions and chemical composition.

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The most common watch battery type is the silver oxide battery, which powers most quartz watches. These batteries are labeled with a four-digit code, such as SR626, SR920, or SR44. The first two digits (SR) indicate the battery chemistry—in this case, silver oxide. The last two digits describe the physical size. For example, an SR626 has a diameter of 6.8 millimeters and a thickness of 2.6 millimeters. An SR920 is larger, with a 9.2-millimeter diameter and 2.0-millimeter thickness.

Alkaline batteries also power some watches, though they are less common in modern timepieces. These are typically labeled with codes like LR626 or LR44. The LR designation means alkaline, and they follow the same sizing convention as silver oxide batteries. Alkaline batteries generally last shorter in watches compared to silver oxide alternatives.

Mercury batteries were once standard in watches but are now banned in most countries due to environmental concerns. If you have an older watch that originally used a mercury battery, a replacement will need to use a modern alternative like silver oxide instead.

• Silver oxide batteries power most modern quartz watches
• The four-digit code tells you both the battery type and size
• Alkaline batteries are available but less common for watches
• Older watches designed for mercury batteries need alternative replacements

Practical Takeaway: Before purchasing a replacement battery, locate your watch's battery compartment and note the exact code printed on the old battery. This code is your key to finding the correct replacement.

How to Find Your Watch Battery Size

Finding your watch's battery size requires opening the case back and examining the old battery. Most watches have a removable case back held in place by a small screw or by a snap-fit design. If your watch is waterproof, opening it yourself may void its water resistance rating, so you may want to consider having a professional jeweler or watch repair shop handle this step.

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If you decide to open the case yourself, you will need a case back opener tool, which costs just a few dollars and is available online or at jewelry supply stores. Gently insert the tool into the slot on the case back and turn counterclockwise until the back loosens. Remove it carefully to avoid damaging the threads.

Once the case is open, you will see the battery sitting in its compartment. The battery code is printed on the top surface. Write this code down exactly as it appears—including all letters and numbers. If the code is hard to read due to wear or dirt, you can gently clean the battery's surface with a dry cloth.

If your watch does not have a removable case back, it may have a snap-off design. Look around the edges of the case back for small indentations or tabs. Using a thin, flat tool like a butter knife, gently pry at these points to release the back. This requires patience and care to avoid scratching the watch.

For some vintage or expensive watches, the case back is sealed and requires professional tools to open safely. In these cases, consulting a watch repair specialist is the better choice.

• Most watches have a removable case back secured by a screw
• A case back opener tool makes this process easier and safer
• Always write down the exact battery code before replacing the battery
• Waterproof watches may need professional service to maintain their rating
• Snap-fit case backs require gentle prying at the edges

Practical Takeaway: Keep the case back opener tool in your watch maintenance kit. Investing in this inexpensive tool lets you handle future battery replacements without needing a repair shop visit.

Common Watch Battery Sizes Explained

Understanding the most common battery sizes helps you recognize what your watch might need. The SR626 is one of the most frequently used batteries in watches. It powers many everyday watches from major brands and measures 6.8 millimeters in diameter with a thickness of 2.6 millimeters. If you have a typical analog watch bought in the last ten years, this is a likely candidate.

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The SR920 is a larger battery used in watches that need more power, such as those with additional complications like a date window, day display, or chronograph function. Its 9.2-millimeter diameter makes it noticeably larger than the SR626. Despite being bigger, it is still quite small and fits in watches that look similar in size to those using smaller batteries.

The SR927 is another common size, measuring 9.2 millimeters by 2.7 millimeters. This battery powers many mid-range watches and works well in timepieces with modest power demands. The slightly increased thickness compared to the SR920 affects where it can fit.

The SR44 is a particularly common battery that appears in many inexpensive and mid-range watches. It has a larger 11.6-millimeter diameter, making it one of the more substantial watch batteries. Despite its size, it still delivers the low voltage typical of all watch batteries.

The LR626 and LR44 are alkaline alternatives to the silver oxide versions listed above. An LR626 can sometimes substitute for an SR626, but the alkaline version typically lasts only 40 to 60 percent as long. Checking your watch manual or the old battery code ensures you get the right type, not just the right size.

• SR626: 6.8mm diameter, 2.6mm thickness—very common
• SR920: 9.2mm diameter, 2.0mm thickness—for more complex watches
• SR927: 9.2mm diameter, 2.7mm thickness—mid-range watches
• SR44: 11.6mm diameter, 2.6mm thickness—larger watches
• LR variants exist for each size but have shorter lifespans

Practical Takeaway: Save any old batteries from watches you own. Over time, you will recognize which sizes you need most, and this reference collection helps you identify batteries quickly when replacements are needed.

Reading and Decoding Battery Size Codes

The four-digit battery code system is logical once you understand how it works. The first two characters always indicate battery chemistry. SR means silver oxide, LR means alkaline, PR means zinc-air, and CR means lithium. Understanding this first part tells you what type of battery you are looking at and what alternatives might work as substitutes.

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The last two digits encode the physical dimensions using a specific formula. The first of these two digits represents the diameter in millimeters, while the second digit represents twice the height in millimeters. For example, an SR626 breaks down as: SR (silver oxide), 6 (6.8 millimeters diameter when you add 0.8), and 26 (2.6 millimeters height). This system is not perfectly linear, which is why you cannot simply guess dimensions from the code—you must look them up or refer to a battery size chart.

Some batteries have additional markings beyond the four-digit code. You might see voltage information, such as 1.55V for silver oxide batteries. You might also see manufacturing date codes or brand names. None of these extras change how you identify the correct replacement; the four-digit code remains your primary identifier.

Occasionally, you will encounter older watch batteries with different naming systems. Some vintage watches use codes like MS626 or SR1154W. These variations follow similar logic but may require a reference guide to decode accurately. If you encounter an unfamiliar code, searching that code online with the word "battery" will show you equivalent modern options.

Understanding this system prevents costly mistakes. Purchasing an SR927 when you need an SR626 will not work—the battery will not fit properly in the compart