The Ultimate Revelation Of CMOS Battery

CMOS Battery(Complementary Metal Oxide Semiconductor) is a simple lithium cell battery. This provides power to CMOS chip of a computer to maintain some values like date, time, and other hardware settings. These will be used again when the system gets booted.

But to clearly understand CMOS, we must first understand BIOS(Basic Input/Output System). BIOS is a system that carries out some important functions in the computer.

It manages the input and outputs commands of the computer effectively mainly during booting the system. Every input is given and output received is a task of BIOS.

CMOS battery

BIOS needs to be functional even the power source is not connected to it. This is achievable only when CMOS battery supplies power to BIOS so that basic system functions are not affected.

It lasts anywhere between two to ten years from the time of manufacture. It has a coin-like shape and can be found to be found both in laptop and desktop systems.

However, it is used frequently in laptops than desktops because laptops are unplugged for a longer time comparatively.

CMOS Battery function

The major function is to provide power supply to CMOS chip in turn to BIOS to ensure that basic system functions are carried out even when the system is not connected to a power source.

Have you ever wondered how the computer/ PC shows the correct time and date and maintains all hardware settings as it is even after you have booted the system after a long time?

The hero behind this is CMOS battery that ensures the required power supply and keeps the functions running.

CMOS Battery Voltage

It ranges from 3V to 5V. But most commonly used CMOS batteries are of 3V, however, there are some devices we can come across a CMOS battery of 5V.

Is it chargeable?

It is not chargeable. When the computer is connected to a power source, CMOS chip draws power from motherboard whereas when it is not connected to a power source, CMOS chip draws power from this battery.


The maximum lifespan of CMOS batteries was not more than three years in the early years however it is much better now.

The lifespan is anywhere between two years to ten years based on the usage. If you keep the power source connected to the system more then the CMOS battery is not used much so its lifespan increases.

However, if you tend to keep the power source unplugged, CMOS battery is used more and the lifespan of this will be less. So it depends on the user. In any case, it may need replacement after ten years of time.

Signs of damage in CMOS battery

Typical symptoms of a cmos battery failures are – 

Incorrect date and time

If there is damage then one of the early signs would be the display of incorrect date and time. BIOS uses CMOS battery to keep these basic system functions running if there is a damage, BIOS will not be able to perform these functions accurately.

Trouble booting

With a damaged CMOS battery, BIOS will not be able to perform the booting function properly and you might notice trouble with it.

Or in some cases, the system may not boot up at all. You can also observe a constant beep from the motherboard.

Peripherals respond incorrectly

The keyboards key do not respond, you might face trouble using the cursor, the system functions may not respond properly and customized keyboard settings may have reset by itself.

All these are the result of damaged CMOS battery as BIOS is responsible for peripheral functions and has trouble in carrying them out.

Hardware drivers have disappeared

Hardware drivers that you might have installed on the computer/ laptop would have disappeared without you initiating anything. This is a major sign of damage.

In such cases, you will have to again download and install them but there are high chances of them disappearing again if the damaged battery is not replaced.

Trouble connecting to the internet

CMOS battery failure will also have an impact on the ability to connect to the internet as BIOS maintains both hardware and network drivers.

Replace CMOS battery

How to remove CMOS Battery?

The process of replacing it is a quite simpler process. It only requires a new CMOS battery, screwdriver, ESD mat, and compressed air.

  1. Shut down the laptop and drain the battery out by long press on the power button.
  2. Open the laptop casing using a screwdriver and remove it. Also, remove the battery to prevent the laptop from turning on when your working.
  3. Take out the damaged CMOS battery, it is a coin like in shape and easily removable.
  4. Place the new battery in the same location.
  5. Insert the laptop battery and attach the laptop case as it was earlier.
  6. Turn on the laptop. The basic settings would have gone back to its original settings. Reset everything again as per your requirement.

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