# How CMOS battery can prevent random shut down of computer ?



## bindudhindsa (Mar 3, 2007)

Hello Friends, 

This is not a question so just curious about something. I was fixing a laptop on weekend. Problem was it just shut down itself after 3-4 minutes. Ofcourse my first thought was processor heating up. So i opened the laptop, removed all the dust ( it was lot of dust on heat sink !! ). I tried again and it was showing same problem. I checked the processor for thermal paste, applied some paste and tried again but still shutting down after few minutes of running.

One of my friend suggested me to replace CMOS battery (as per his past experience), i had a doubt about it but i had no choice at that point so as he suggested i changed the CMOS battery. To my surprise its working fine after that.

Just curious to know how CMOS battery had to do anything with the shutting down of computer ??? 

Please share your experience in here .. 

THanks 
Pal


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## greenbrucelee (Apr 24, 2007)

the cmos battery is a major part of the motherboard without one or one that is failing the computer will not work.


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## bindudhindsa (Mar 3, 2007)

Yes i can understand that part greenbrucelee but i have never experienced shutting down of computer just because of failing CMOS battery. I know resetting of BIOS, windows drivers or few other symptoms are linked with CMOS battery. But do you think it has to do anything with shutting down the computer after few minutes


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## greenbrucelee (Apr 24, 2007)

I have seen it happen lots of times.

if the cmos battery isn't working then the motherboard can't POST because it's like to the BIOS.


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## bindudhindsa (Mar 3, 2007)

I m sorry greenbrucelee but i did't understand what does it mean when you said " motherboard cant POST because its like to the BIOS" . I did't have any problem in starting up .. i was trying to do clean install using windows installation disc and whenever it reached format screen and starts formatting .. it just shut down itself without any warning but after CMOS battery replacement i finished everything so nicely.


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## MonsterMiata (Jan 5, 2010)

Here is a page explaining why and how batteries fail.

http://www.batteryeducation.com/2006/04/battery_degrada.html

The battery could work at first but as its exposed to more heat i would think it starts to break down to the point where the transfer of power is interrupted causing a shutdown.


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## greenbrucelee (Apr 24, 2007)

MonsterMiata said:


> Here is a page explaining why and how batteries fail.
> 
> http://www.batteryeducation.com/2006/04/battery_degrada.html
> 
> The battery could work at first but as its exposed to more heat i would think it starts to break down to the point where the transfer of power is interrupted causing a shutdown.


exactly.


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## bindudhindsa (Mar 3, 2007)

Thanks for your reply Guys, that was really useful information about the batteries but i am sorry to say that we are just moving away from my point where i started. This discussion was not for why and how battery fails ?

My question was " does CMOS battery failing could cause shut down of computer after running for few minutes"


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## Wrench97 (May 10, 2008)

Not that I've ever seen, it may cause it not to start, but once powered up it should continue to run.


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## Invert (Apr 1, 2010)

This guy seems to state it here ; http://www.ehow.com/i/#article_5011717


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## Amd_Man (Jan 27, 2009)

A failing or failed cmos battery will not cause a computer to shut down or reboot. Ive never ever seen a computer not boot up because of a failed cmos battery. What will happen is that you get a checksum error message and you must either load setup defaults or enter bios and re-enter all the information before you can load Windows. That will continue over and over untill the Cmos battery is replaced.


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## Amd_Man (Jan 27, 2009)

MonsterMiata said:


> Here is a page explaining why and how batteries fail.
> 
> http://www.batteryeducation.com/2006/04/battery_degrada.html
> 
> The battery could work at first but as its exposed to more heat i would think it starts to break down to the point where the transfer of power is interrupted causing a shutdown.


A Cmos battery only trickles power to save Bios settings when the computer is powered off. Not when the computer is powered on.


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## MonsterMiata (Jan 5, 2010)

Invert said:


> This guy seems to state it here ; http://www.ehow.com/i/#article_5011717


Good info. I don't think you can say a failing cmos battery would not cause his symptoms if he replaced it and it fixed the problem. Looks to me like on his motherboard the cmos is linked to more than just the bios settings. If the battery starts to break down under stress it wont provide a proper connection and the motherboard will shut down.


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## MonsterMiata (Jan 5, 2010)

bindudhindsa said:


> Thanks for your reply Guys, that was really useful information about the batteries but i am sorry to say that we are just moving away from my point where i started. This discussion was not for why and how battery fails ?
> 
> My question was " *does CMOS battery failing could cause shut down of computer after running for few minutes*"


It seems to be so in your case because your cmos battery sounds like its linked to more than just the bios settings.


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## Amd_Man (Jan 27, 2009)

I've been doing this for many many years and I've never seen a Cmos battery cause a shut down.


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## greenbrucelee (Apr 24, 2007)

I have seen it happen or thats what I thought it was on a 486 DX-2 and a p3


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## Amd_Man (Jan 27, 2009)

A Cmos battery is only used to save the Bios settings when the computer is power down. I've never seen or heard of a failing or failed battery cause a system shut down. Like they say though, " there's a first time for everything".


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## MonsterMiata (Jan 5, 2010)

Amd_Man said:


> I've been doing this for many many years and I've never seen a Cmos battery cause a shut down.


Just because you have never physically seen it does not mean you can rule out the possibility as a whole. Iv never seen a Maserati but that does not mean it does not exist. Gota keep an eye open for all possibilities no matter how far fetched or dumb it may seem. Not trying to make an argument just in case anyone takes it that way. Just be open minded :grin:


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## MonsterMiata (Jan 5, 2010)

Amd_Man said:


> A Cmos battery is only used to save the Bios settings when the computer is power down. I've never seen or heard of a failing or failed battery cause a system shut down. Like they say though, " there's a first time for everything".


Yup :laugh:


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## greenbrucelee (Apr 24, 2007)

Amd_Man said:


> A Cmos battery is only used to save the Bios settings when the computer is power down. I've never seen or heard of a failing or failed battery cause a system shut down. Like they say though, " there's a first time for everything".


yeah its funny because when I had those systems and experienced the issue myself replacing the battery was the only thing that sorted it.


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## bindudhindsa (Mar 3, 2007)

Thanks for this discussion guys so we cant rule out this possiblity that failing CMOS battery can cause shut down of the computer. Anyways i learnt a lot from this discussion. Thanks again


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