Laptop CMOS Battery
Laptop CMOS Battery

Need to refresh the CMOS battery in your Acer, Dell, Lenovo, HP, or other laptop? Dive into this easy-to-follow guide, detailing each step to ensure a seamless battery replacement process. But before we learn about changing out the CMOS battery on your laptop, a slight clarification that can clear up some confusion:

Not all laptops have removable CMOS batteries!

In fact, most modern laptops have a soldered on RTC battery and the EFI settings are stored in non-volatile flash RAM. So if you are going to swap out the CMOS battery, first make sure that your laptop does in fact have one that can be taken out and then verify that you have a replacement for the battery type that is in there. Between soldered on options and proprietary battery layouts it has become less and less a thing to do this repair – but if you’re one of the lucky few with the option available to you continue on.

laptop cmos battery close up

What Is A CMOS Battery?

The CMOS (Complementary Metal-Oxide Semiconductor) battery, though small, plays a crucial role in preserving the BIOS settings of your laptop. Over time, this battery can deplete, causing system time resets or BIOS-related errors. Fear not! Here’s how you can adeptly replace the CMOS battery in your laptop.

Understanding the Importance of CMOS

This tiny battery maintains the internal clock and system settings. When it begins to fail, you might notice incorrect system time or date, and sometimes even boot-up issues. Recognizing these signs is the first step in addressing the issue.

Do Modern Laptops with Fixed Batteries Still Need a CMOS Battery?

In today’s technological landscape, laptops are evolving with fixed batteries, primarily driven by the demand for sleeker and lighter designs. Traditionally, computers (desktops and laptops) were equipped with a CMOS battery. Its primary function was to operate the real-time clock (RTC) and, in some instances, retain BIOS settings. Most laptops with removable batteries feature a CMOS battery, ensuring the clock settings are intact even when the main battery is detached momentarily.

Why CMOS Batteries Still Matter:

While laptops with fixed batteries are rechargeable, they can’t retain charge indefinitely. However, CMOS batteries differ in nature. Imagine leaving your device idle for a month, only to find the BIOS settings lost when you return – a frustrating scenario, right?

Although flash storage mediums exist that don’t require continuous power, they deteriorate with repeated read-write operations. Surprisingly, BIOS undergoes frequent reads and writes, making the CMOS battery indispensable.

While technology continues to evolve, we might one day see rechargeable batteries with extended power retention or innovative BIOS storage solutions. However, until such breakthroughs are mainstream, the humble CMOS battery remains a cost-effective and reliable choice.

The Modern OS and RTC Dependency:

Modern operating systems heavily rely on the RTC. If the primary battery depletes, a backup power source is essential for the RTC to function. Hence, a separate battery (like CMOS) becomes critical.

While BIOS settings now reside in non-volatile memory, negating the CMOS’s role, the CMOS battery still holds significance. It ensures accurate time tracking when your computer is off, saving users from resetting the clock after every reboot.

While some argue that PCs can auto-adjust the time via Network Time Protocol (NTP) servers upon reboot, such servers aren’t always accessible. Moreover, misalignment in RTC can result in booting issues, causing operational disruptions.

Guide to Replacing the CMOS Battery in Laptops

Assuming your laptop battery is detachable, follow these steps:

  1. Prepare the Workspace: Ensure you have a clean, static-free workspace. Lay your laptop on a soft cloth to prevent scratches.
  2. Switch Off and Unplug: Power off the laptop, unplug the charger, and remove the main battery if it’s externally accessible.
  3. Open the Back Panel: Using a suitable screwdriver, carefully remove the screws holding the laptop’s back panel. Gently lift the panel to expose the internal components.
  4. Locate the CMOS Battery: The CMOS battery is typically a coin-cell battery, resembling a watch battery. It might be held in place by a plastic clip.
  5. Gently Remove the Old Battery: Using a plastic tool or your fingernail, gently release the battery from its holder, ensuring you don’t damage any nearby components.
  6. Insert the New Battery: Place the new CMOS battery in the holder. Ensure it’s securely seated and the positive side faces upwards.
  7. Reassemble Your Laptop: Carefully place the back panel in its original position and tighten the screws. Re-insert the main battery if you had removed it.
  8. Power On and Reset BIOS (if necessary): Turn on your laptop. You might need to enter the BIOS to reset the date and time.

Safety and Precautionary Tips

  • Handle with Care: Always handle your laptop and its components with care. Avoid using excessive force.
  • Static Precautions: Consider using an anti-static wristband to prevent static damage to your laptop’s components.
  • Use the Right Tools: Ensure you’re using the correct size screwdriver to avoid stripping the screws.


  • How do I know the exact CMOS battery type required for my laptop? Typically, laptops use a CR2032 battery, but always refer to your laptop’s manual or the label on the old battery to confirm.
  • How often should the CMOS battery be replaced? CMOS batteries usually last 3-5 years, but if you notice BIOS-related issues or time resets before then, consider checking the battery.
  • Can I use any brand of CMOS battery? While the type (e.g., CR2032) is standard, it’s recommended to use reputable brands for longevity and reliability.

Conclusion: A Fresh Start for Your Laptop Replacing the CMOS battery in your laptop can seem daunting, but with the right steps and precautions, it’s a straightforward process. Now, with a new battery in place, your laptop is ready to keep time and settings accurately for years to come.

Although the term “non-removable battery” suggests permanence, these batteries are always detachable – just less user-friendly in terms of access. As for the CMOS battery, its modest yet crucial role in modern laptops seems set to continue for the foreseeable future.

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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