What Is CMOS Battery, BIOS? How Do These Work? How To Clear CMOS? How To Replace It? FAQs

All of us like to use different types of gadgets like smartphones, watches, calculators, cameras, etc. in our daily lives. Out of all the gadgets, some of the most used gadgets are smartphones and laptops. In smartphones and laptops, a battery is being used to operate these gadgets. But do you know that our laptops have more than one battery?

In A Laptop, How Many Batteries Are Used?

Two batteries are used in every laptop. One is the main battery, which is basically used to operate the laptop. It is a chargeable battery and can be charged by its charger through a power supply. The other is the CMOS battery, which is used to power the BIOS firmware in the laptop. Let us know deeply about the CMOS battery.

CMOS Battery

CMOS stands for "Complementary Metal Oxide Semiconductor". CMOS is a basic coin-sized CR2032 battery attached to the motherboard of our laptop and used to store the BIOS settings. It is also called Real Time Clock (RTC), Non-Volatile RAM (NVRAM), CMOS RAM, Non-Volatile BIOS memory, or Complementary Symmetry Metal Oxide Semiconductor (COS-MOS). As it powers the BIOS and is used to store BIOS information, before getting more information about the CMOS battery, we must have information about the BIOS. Like, what is BIOS? How does BIOS work?

What is BIOS?

BIOS stands for "Basic Input/Output System." A BIOS is a firmware pre-programmed by the laptop manufacturer while manufacturing the laptop. The BIOS is programmed by the manufacturer by using some lines of code contained in a chip that is attached to the motherboard. It is the first program to run on every computer. Essentially, BIOS assists us in installing the operating system and connecting it to hardware by identifying and configuring the hardware.

The BIOS's Role In The Boot Process

The BIOS provides the essential support required for the computer during the startup or boot process. After identifying the hardware in computers, BIOS configures it and connects it to the operating system, which is either pre-installed by the manufacturer or installed by us. The whole process is known as the "boot process."

How Does BIOS work?

BIOS works through an input and output model, which can be understood by an example. Let us open and run any software on our computer, and as the CPU works as the brain of the computer, it receives information about that software (input). Now the CPU sends the command to the hard disc installed on the computer. Now the hard disc collects stored data about that software and sends it to the CPU (output). The CPU runs the software and sends the information related to images that have to be created to the graphics processor (input). Now graphics work on information and send instructions regarding the arrangement of pixels to create images to monitor. Now the monitor works on it and creates all the images. (Output).

Use Of CMOS Battery

Basically, a CMOS battery is used to store the date, time, and other BIOS settings. Whenever we shut down our computer for a certain time period, After that time, when we shut off the computer, it shows us the exact time and date. This is because the CMOS battery keeps running even if we unplug the computer or shut the laptop, and stores the information related to date and time. That is why it is also called a "Real Time Clock" (RTC). The CMOS battery is used in both laptops and desktops but is mostly used in laptops because the laptop remains unplugged for a long time.

How Does The CMOS Battery Get Charged?

Whenever we plug in the charger and connect the laptop to the power supply, it gets charged. Whenever we unplug the charger, it gets discharged.

CMOS Battery Lifetime

Most CMOS batteries have a life of 2 to 10 years. Furthermore, it depends on the plug-in time for the laptop. The more you use your laptop, the longer the battery will last.

CMOS Battery Voltage

Most CMOS batteries range from 3V to 5V. In most devices, 3V CMOS batteries are used, and in some devices, 5V CMOS batteries are used.

How to Identify CMOS Battery Failure?

There are the following symptoms to be checked to identify CMOS battery failure:

Difficulties With Boot Up

If you are facing any issues while booting up your computer, it means the CMOS battery has failed.

Constant Beeping Sound While Bootup

If while booting up there is a constant beeping sound coming from the motherboard, it is caused by a CMOS battery failure.

Incorrect Date and Time

As we have already discussed, the CMOS battery stores the date and time while the computer remains shut down, but in the case of CMOS battery failure, the date and time will not be stored and the wrong date and time will appear on the computer.

Dis-Functions Of The Keyboard

You can face issues while moving your cursor, clicking on any icon, and the laptop will be unable to read your keyboard inputs. If you made changes to your keyboard settings, they will be reset to their default.

Drivers Disappearing Or Being Uninstalled

If you have installed any drivers on your computer, they will disappear because of CMOS battery failure. In such a case, you have to re-install the drivers.

Issues While Connecting To The Internet

You may face issues while connecting to the internet.

How to Clear CMOS?

There are three methods to clear the CMOS:

Reset BIOS Settings To Default

The easiest way to clear CMOS is to "reset BIOS settings to default". To do so, follow these steps:
 
Firstly, power off the laptop.
 
Open the BIOS setup menu and then choose to reset the BIOS settings to default. The option can be written as "reset to default," "factory default," "clear BIOS," "load setup defaults," etc.
 
Now choose the save option and then restart your computer.

Clear CMOS By Jumper Method

You can also clear CMOS using the jumper method. To do so, follow these steps:
 
Shut down your computer.
 
Unplug all power sources.
 
Remove all screws by using a screwdriver.
 
Remove the case of the computer so that the motherboard will appear.
 
Now find the CMOS jumper. The CMOS jumper is three pins and is usually located near the battery.
 
Usually, there are 1–2 and 3–4 positions for jumpers. To clear the CMOS, remove the jumper and place it in the next position.
 
Now wait for five minutes and then place the CMOS jumper in the first position again.

Clear CMOS By Removing The CMOS Battery

You can also clear CMOS by removing the CMOS battery. To do so, follow these steps:
 
Shut down your computer.
 
Unplug all power sources.

Remove all screws by using a screwdriver.

Remove the case of the computer so that the motherboard will appear.
 
Now find the CMOS battery on the motherboard. It may be in a vertical or horizontal battery holder or may be connected to the motherboard via wire.
 
If the CMOS battery is still in the holder, note the - and + orientations before disconnecting it from its connectors and removing it. If the CMOS battery is connected to the motherboard via a wire, disconnect the wire and remove the battery.
 
Wait for five minutes.
 
Now reconnect the battery and put the computer case back together. Screw up the screw and connect the computer to the power source.
 
When you remove the CMOS battery, there is no power supply to it and it turns off. Because of this, all the data stored in it will be clear.

How To Replace The CMOS Battery?

You can replace the old CMOS battery with a new CMOS battery by following these methods:
 
Choose a perfect place (hard or flat surface, with a conductive foam pad) to prevent electrostatic discharge. because electrostatic discharge can damage components of the computer.
 
* Rub your hand on a metal surface to get rid of the charge, or wear an anti-static wrist band.
 
Shut down your computer.
 
Unplug all power sources.
 
Remove all screws by using a screwdriver.
 
Remove the case of the computer so that the motherboard will appear.

Now find the CMOS battery on the motherboard. It may be in a vertical or horizontal battery holder or may be connected to the motherboard via wire.

If the CMOS battery is in the holder, then note the "- and +" orientations. Disconnect it from its connectors and remove it. If the CMOS battery is connected to the motherboard via a wire, disconnect the wire and remove the old battery.
 
Now place the new CMOS battery in place of the old one.
 
Now put the computer case back together, screw up the screw, and connect the computer to the power source.