CMOS Battery
CMOS Battery

Explore the unsung hero of your computer – the CMOS battery. Dive into its definition, purpose, and impact on your computer’s performance.

Introduction: A Sneak Peek into Computer’s Inner Workings

You’ve probably heard about components like the CPU, RAM, and hard drive that keep your computer running smoothly. But have you ever wondered about the lesser-known parts, like the CMOS battery? This small component plays an essential role in your computer’s functionality.

Defining the CMOS Battery: The Basics

CMOS stands for Complementary Metal-Oxide-Semiconductor. The CMOS battery, a small, circular cell, powers the CMOS memory that stores BIOS settings and system time and date information.

The CMOS Battery’s Role in Maintaining BIOS Settings

BIOS (Basic Input/Output System) is the software your computer uses to start the operating system and manage data flow between the system’s hardware devices. The CMOS battery provides power to the CMOS chip, preserving these BIOS settings even when the computer is turned off or unplugged.

How CMOS Battery Powers Real-Time Clock

The CMOS battery also powers the real-time clock (RTC), a component that keeps track of the current time and date. Even when your system is powered off, the RTC keeps ticking, ensuring that your computer always knows the correct time when it powers back on.

Identifying a Failing CMOS Battery

When a CMOS battery is nearing the end of its lifespan, it may not adequately maintain BIOS settings or the RTC. Symptoms can include your computer losing track of time or returning to default BIOS settings after being powered off.

The Lifespan of a CMOS Battery

A typical CMOS battery can last several years, sometimes even outliving the computer it’s installed in. However, its lifespan can vary based on usage patterns and the specific battery model.

Replacing a CMOS Battery: A Simple Process

Replacing a failing CMOS battery is a relatively straightforward process. You can usually find the battery on the computer’s motherboard, and it’s typically a standard CR2032 lithium cell that you can purchase at most electronics stores.

Impact of CMOS Battery Failure on System Performance

If the CMOS battery fails, it won’t affect the performance of your computer while it’s running. However, you may have to reset the time and date or adjust BIOS settings each time you boot up your system, which can be a significant inconvenience.


How do I know if my CMOS battery is failing?

If your computer constantly loses track of time or resets to default BIOS settings, it could be a sign that your CMOS battery is failing. Other symptoms could include system instability or error messages on startup related to the BIOS or CMOS.

Can a computer run without a CMOS battery?

Yes, a computer can still run without a CMOS battery. However, it may lose track of the current time and date and default BIOS settings when powered off, which can be inconvenient and disrupt certain functions.

Is it safe to replace the CMOS battery myself?

Yes, replacing the CMOS battery is a relatively simple process, and most people can do it themselves. However, remember to turn off and unplug your computer before you begin to avoid any potential electric shock.

What kind of battery is a CMOS battery?

The most common type of CMOS battery is the CR2032 lithium cell, a 3-volt battery that you can find at most electronics or general retail stores.

What happens when the CMOS battery dies?

When the CMOS battery dies, your computer will lose its ability to maintain the current time and date and remember BIOS settings when powered off. However, this won’t impact your computer’s performance while it’s running.


In the grand scheme of your computer’s inner workings, the CMOS battery might seem insignificant. However, this small component is crucial for preserving BIOS settings and maintaining the system’s real-time clock. Understanding its function can help you troubleshoot potential issues and keep your system running smoothly.

Eric Chan

Hi! I’m Eric and I work on the knowledge base at  You can see some of my writings about technology, cellphone repair, and computer repair here.

When I’m not writing about tech I’m playing with my dog or hanging out with my girlfriend.

Shoot me a message at if you want to see a topic discussed or have a correction on something I’ve written.

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