LR66 Battery Equivalent: Complete Guide

The LR66 battery is a compact, dependable, and widely available alkaline button cell that powers countless small devices around us. Its common equivalents — AG4, LR626, and SR626SW — make it easy to find replacements globally.

If you’ve ever opened a watch, calculator, or small electronic toy and found a tiny silver button cell inside, chances are you’ve come across an LR66 battery. Despite its small size, this compact power source plays a critical role in many precision devices. Yet, many people get confused when searching for LR66 equivalents, since it can be labeled under several different codes depending on the brand or chemistry.

This guide will explain everything you need to know about the LR66 battery, including its dimensions, specifications, equivalents, common uses, and how to select the right replacement safely.

Overview of LR66 Battery 

What is an LR66 Battery?

The LR66 is a small, alkaline button cell battery designed for low-drain, long-lasting electronic devices. It is part of the LR series of alkaline coin cells, which are commonly used in watches, small toys, thermometers, and digital gadgets.

The designation “LR” refers to alkaline manganese dioxide chemistry, while the “66” represents the battery’s size code defined by the IEC (International Electrotechnical Commission).

Dimensions

● Diameter: 6.8 mm

● Height: 2.6 mm

● Shape: Cylindrical button cell

● Weight: Approx. 0.3 – 0.4 grams

These compact dimensions make the LR66 ideal for miniature electronic devices where space is limited.

Voltage

● Nominal Voltage: 1.5 Volts

● Cut-off Voltage: Around 1.0 Volt

The voltage remains fairly stable during most of the battery’s life, ensuring consistent device performance until it approaches full discharge.

Capacity

● Typical Capacity: 25–32 mAh (depending on manufacturer and discharge rate)

The capacity can slightly vary across brands and storage conditions. For instance, a high-quality brand like Duracell or Energizer may offer a bit higher capacity and longer shelf life compared to generic models.

IEC and Other Codes

The LR66 battery can appear under multiple names depending on the manufacturer or standardization system. Here are its common equivalents:

Note: The most common cross-reference for LR66 is AG4 or LR626. These are often interchangeable in most devices.

Key Features of LR66 Battery

Despite being tiny, the LR66 battery offers several notable features that make it suitable for a variety of compact electronic applications.

1. Stable Voltage Output: The LR66 provides a consistent 1.5V output for most of its discharge cycle, which ensures reliable device operation.

2. Compact Size: Its small form factor fits perfectly in slim devices like watches or small sensors.

3. Affordable and Widely Available: Alkaline button cells like the LR66 are cost-effective and can be found in most electronic or convenience stores.

4. Good Shelf Life: When stored properly (in a cool, dry place), LR66 batteries can last up to 3–5 years without significant capacity loss.

5. Mercury-Free Composition: Modern LR66 cells are made without toxic mercury, making them safer and more environmentally friendly than older models.

6. Reliable Performance in Low-Drain Devices: Ideal for small devices that don’t require high current draws, such as clocks, thermometers, and calculators.

Technical Specifications

Here’s a quick summary of the LR66 battery’s technical parameters:

What is a LR66 Battery Used For?

LR66 batteries are widely used in compact, low-drain devices. Their small size, stable output, and affordability make them a go-to choice for consumer electronics.

Typical Applications:

7. Analog and Digital Watches Many quartz watches use LR66 or its silver oxide equivalent (SR626SW) for timekeeping.

8. Calculators Provides steady voltage for calculator displays and internal circuits.

9. Laser Pointers Powers low-energy laser diodes.

10. Small Toys and Keychain Gadgets Common in LED mini flashlights, sound-producing toys, or novelty keychains.

11. Medical Devices Used in small diagnostic devices such as digital thermometers or blood glucose meters.

12. Laser Sights and Compact Sensors Occasionally found in miniature sensors, remote controls, or hearing amplifiers.

What is the Equivalent Battery to LR66?

The most common equivalent batteries to the LR66 include:

● AG4

● LR626

● 177

● V36A

● SR626SW (Silver Oxide)

● SR66

These are compatible replacements that share nearly identical dimensions and voltage characteristics.

1. LR626 / AG4 (Alkaline)

The LR626 and AG4 are direct alkaline equivalents of the LR66. They are essentially the same cell under different naming systems.

● Voltage: 1.5V (same as LR66)

● Capacity: Around 28–32 mAh

● Size: 6.8 × 2.6 mm

● Chemistry: Alkaline

 Interchangeability: These can be used interchangeably with LR66 in any device that fits the size and voltage requirements.

2. SR626SW (Silver Oxide)

The SR626SW (sometimes called 376 or SR66) is a silver oxide version of the LR66. While it has the same dimensions, the chemistry offers higher energy density and more stable voltage.

Compatibility: The SR626SW can safely replace LR66 in most devices, especially in precision instruments like watches, since its stable voltage ensures more accurate performance.

Minor Difference: While both are compatible, the SR626SW provides a bit higher voltage and longer life. It is a premium alternative and preferred when consistent power is required.

3. Other Possible Equivalents

Safety Tips for Using LR66 Batteries

While small and low-voltage, button batteries require careful handling, especially around children and sensitive electronics.

1. Avoid Mixing Old and New Batteries

Using mixed batteries can cause leakage or uneven discharge, which can damage devices.

2. Store in a Cool, Dry Place

Heat and humidity can reduce capacity and increase the risk of corrosion.

3. Keep Away from Children

Button batteries are a choking hazard. If swallowed, they can cause severe internal burns. Always keep them out of children’s reach.

4. Check Polarity

Ensure the positive (+) and negative (-) sides are aligned correctly when inserting.

5. Do Not Recharge

LR66 batteries are non-rechargeable. Attempting to recharge them can cause leakage or explosion.

6. Dispose Properly

Recycle used button cells through proper e-waste channels. Do not dispose of them in fire or general trash.

Common Problems & Troubleshooting

Even though LR66 batteries are generally reliable, a few common issues can occur. Here’s how to handle them.

1. Device Not Turning On

● Possible Cause: Dead or incorrectly inserted battery.

● Fix: Check polarity, clean battery contacts, and replace with a new LR66 or SR626SW cell.

2. Short Battery Life

● Possible Cause: Using an alkaline cell (LR66) in a high-drain device.

● Fix: Switch to a silver oxide version (SR626SW) for longer life.

3. Leakage

● Possible Cause: Over-discharge or exposure to heat.

● Fix: Replace battery immediately and clean contacts with isopropyl alcohol.

4. Corrosion on Contacts

● Possible Cause: Moisture exposure during storage.

● Fix: Clean contacts with a cotton swab and dry thoroughly before use.

5. Inconsistent Device Performance

● Possible Cause: Battery nearing end of life or low-quality generic cell.

● Fix: Replace with a trusted brand like Duracell or Maxell.