How to Test a 377 / SR626SW Watch Battery with a Multimeter

If you have a watch SR626SW battery that isn't working, you may be wondering how to test it. In this post, we'll learn, how to use a multimeter to test the watch battery.We'll also give you some tips on how to extend the life of your watch battery.Keep reading!

Know Your Watch Battery: 377 / SR626SW Basics

SR626SW battery is a small circular silver oxide button battery. It is usually used for color, small electronic bias, especially for watches. The "SR" in the name represents rechargeable tableware oxide, "626" indicates its size (circumference 6.8 millimeters, height 2.6 millimeters), and "SW" indicates its low displacement, suitable for watch operation. 

Features and Characteristics of SR626SW Battery

• Small and compact design
• High energy density
• Stable voltage output
• Long shelf life
• Mercury-free composition
• Non-rechargeable

Technical Specifications of SR626SW Battery

Tools You'll Need

• Digital multimeter (auto-ranging DC volts)
• Mini alligator clips or precision probes
• Load resistor:1 kΩ for quick screening; 3.3 – 10 kΩ for gentler testing
• Clean, lint-free cloth to remove oxidation on contacts

Why a load resistor?

Because a 1k Ω resistor consumes approximately 1.5mA at 1.55V, which is much higher than the μ a level current of a watch. This will exaggerate the voltage drop, expose internal resistance, or cause premature aging.

Step 1: Open-Circuit Voltage (OCV) Test

1. Set the multimeter to DC volts (2 V range or auto).
2. Touch the red probe (+) to the battery's flat top and black probe (–) to the bottom case.
3. Record the reading. A fresh cell should show ≈ 1.55 – 1.60 V with no load.

[Diagram placeholder] Probe placement for measuring 377/SR626SW OCV - top is positive terminal.

Step 2: Loaded Test (With a Resistor)

This method reveals internal resistance and voltage stability under realistic pulse loads.

1. Connect a 1 kΩ resistor across the cell and measure voltage simultaneously.
2. A healthy 377 battery should stay near 1.50 V or higher under load.
3. If voltage drops below ≈ 1.35 V, the cell is weak and should be replaced.

How to Interpret Results (Threshold Table)

Common Mistakes & Real-World Pitfalls

• Confusing chemistries:SR626SW (1.55 V silver oxide) is not the same as LR626/AG4 (alkaline) or CR (lithium 3 V).
• Ignoring drain class:SW for low-drain watches; W for high-drain chronographs.
• Only checking OCV:A battery can show 1.55 V open-circuit but collapse under load.
• Dirty contacts or oxidation:Can mimic a weak battery reading - clean before testing.
• Old stock:Always verify production date and buy from trusted sources.

Recommended Brands & Freshness Checks

Reputable manufacturers such asRenata,Murata (Sony),Maxell,Energizer, andPanasonicmaintain tight tolerances for SR626SW (377) cells. Their datasheets confirm 1.55 V nominal voltage, stable flat discharge curves, and approximately 24–28 mAh capacity per IEC 60086-3 standard.

Common Misconceptions from Online Guides

Several online tutorials describe a simplified process for testing watch batteries with a multimeter - for example, setting the meter to DC voltage, touching the probes to the terminals, and expecting a reading between 1.5 V and 3 V. While this method works for general batteries such as AA, AAA, or CR2032 lithium cells, it's not technically accurate for silver-oxide watch cells like SR626SW / 377.

The SR626SW operates at a nominal voltage of 1.55 V and follows a very flat discharge curve. Even when it's nearly exhausted, it often still shows around 1.50 V on an open-circuit reading. This means a "simple" test that looks only at the voltage can easily misjudge a weak battery as healthy.

To correctly evaluate a watch battery, professionals use a loaded voltage test - applying a resistor (e.g., 1 kΩ) across the terminals while measuring voltage. A good SR626SW will stay above about 1.50 V under load, while a cell that drops to 1.35 V or below is aging or nearly depleted.

FAQs

Is SR626SW the same as 377?

Yes.377is the trade number used by brands like Renata and Energizer;SR626SWis the IEC designation for the same cell type.

Why is the voltage 1.55 V instead of 3 V?

Silver-oxide chemistry produces a nominal 1.55 V. 3 V coins (e.g., CR2032) are lithium cells and much larger.

How often should I replace a watch battery?

For typical analog watches, every 2–3 years. Chronographs or alarm watches may need replacement sooner due to higher drain.