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How to Replace The CMOS Battery

Updated on December 5, 2016
Patkay profile image

Patrick is a dedicated technology writer who wishes to make the world better by informing individuals who seek more knowledge.

Replacing the CMOS Battery of a Computer

The term CMOS is an acronym for Complementary Metal Oxide Semiconductor. The CMOS battery is a coin sized lithium battery responsible for powering the CMOS RAM. The CMOS RAM stores the basic PCs hardware configurations for instance:-
1. Date and time
2. BIOS settings like CPU type, speed, RAM size and type, Plug and play information among others.

Since the CMOS RAM is volatile (will lose all data once powers goes off, as all RAMS do) it must be powered. That is why your PC be it a desktop or laptop requires a CMOS battery. Most desktop computers utilize a coin sized 3 volts lithium battery.

Cmos Battery

Fig 1. CMOS battery
Fig 1. CMOS battery

Signs of a Bad CMOS Battery

When to Change the CMOS Battery

If your computer has a depleted battery, these are some of the signs you are going to experience:

  • BIOS warning:- Some computers are equipped with a BIOS warning that will alert you when your battery's useful life is over or depleted. You will get messages like CMOS check-sum failure, CMOS system options not set among others.
  • Incorrect time and date:- this is a sign you are going to see every time you power on your computer. You will be forced to set the date and time but the moment you turn off your PC, it forgets all the settings. So you will start wondering if your computer is becoming senile. So to avoid that hectic work of setting the date and time every now and then, the best thing is to replace your CMOS battery.
  • The computer can misbehave for instance it can fail to boot completely.

CMOS batteries are cheap and readily available at any electronic or computer shop. They are also long lasting. Once you purchase it, you can replace it by yourself easily but if you are afraid of messing up with your computer, then you can let your technician do it.

Procedure For Replacing The CMOS Battery

To change the CMOS battery, turn off your computer and unplug it from the wall socket. Place it in an area where you will be able to remove the top cover, and where there is enough light so as to be able to see the inside.

There is no way I can tell you how to remove the top cover. This is because it all depends on the computer model that you have, Compaq, dell, HP Compaq, IBM and others, however there is a basic rule that we apply as technicians, 'observe your computer keenly and you will be able to do it'. Some models will have their covers screwed while others it a matter of sliding the cover.

Now, what do you see on the inside after removing the top cover? Accumulated dust covering most of your components? If yes it is because you don't perform regular preventive maintenance on your computer. When is the last time you cleaned your computer on the inside apart from wiping the dust from the outside?

Well, if it is clean, congratulations, keep it like that. Among the hundreds of components connected to your motherboard is the CMOS battery. You should be able to easily identify the CMOS battery. As I had mentioned earlier, it is a coin sized battery (refer to figure 1).

You can now remove the ... wait a minute ... before touching it or any other component, you need to take care of the ESD precautions. To do this assuming you don't have a wrist strap, you will be required to touch the metal casing of your PC. This drains all the excess charges you have in your body so that you end up being at the same potential with your PC. This is just a procedure to protect the components from the effects of Electrostatic Discharge.

Remove The Battery Carefully

Having done that, you can now remove your CMOS battery, carefully, and remember to note how it had been inserted because it has a +ve and -ve side. The +ve side should face upwards. Also remember to check the hooks holding it into position so that you will know how to remove it.

Insert your new CMOS battery correctly and then return the top cover and power on your computer and bingo, you have replaced your CMOS battery. Then adjust your date and time and any other personal settings you might need and you are good to go. No more senile computers in your office/home.

Important Points to Note About the CMOS Battery

  • Do not recharge or dispose off in fire
  • Keep in a cool and dry place
  • Insert battery in right direction
  • Wipe off the battery before using

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How to Change The CMOS Battery

© 2012 Patrick Kamau


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    • Patkay profile image

      Patrick Kamau 6 years ago from Nairobi, Kenya

      Thanks symo, for reading and commenting.

    • profile image

      symo 6 years ago

      thax for educating me