Fly Guy Apr 25, 2015 @ 1:32pm
Weak CMOS Battery May Prevent Your Computer from Booting!
For the last two years I couldn't figure out why my three year old computer wouldn't boot. It wouldn't turn on after a power outage. And even if I did properly shut down the computer the night before, it still wouldn't turn on the next morning. I would have to drain the computer by disconnecting the PSU. At first it was a few minutes, then it gradually took a whole day for the computer to drain, then only would the computer boot up. What confused me was the computer worked like a champ when the computer decided to power on.

Then just last week my computer acted even more strange than what I've described above. The computer would power up after pressing the power button but then it would immediately shut down after two seconds. I looked online and the comments were mostly, "The culprit is most likely the PSU. You need to test your computer with another PSU."

Another person with similar computer issues like me jumped through loops with the advice they gave him online, e.g. re-seat hardware, install another PSU, etc. None worked so he decided to change CMOS battery. The computer then worked like a champ again and has no problem booting. And so did this too work for me. No costly unnecessry PSU, CPU, RAM, MOBO replacement.

Anyone has any theories as to why a weak CMOS battery would prevent the computer from booting and shutting down mid way before a complete boot? It's ridiculous. You will not find this advice on the web that the CMOS battery could be the culprit because as they explain, "The purpose of the CMOS battery is to only hold date and time. A dead or weak CMOS battery will not prevent the computer from booting. You'll just lose date and time."
Last edited by Fly Guy; Apr 25, 2015 @ 1:48pm
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Showing 1-15 of 100 comments
Spyhunter Apr 25, 2015 @ 1:45pm 
It's not too common for people to suffer from dead CMOS batteries as they generally upgrade before they are completely drained. That being said, I've never had an issue with booting with a dead one.

I had to replace a CMOS battery years ago on a P4P800 motherboard (socket 478!), but the only side effect from it being dead was to lose date/time settings as mentioned in your post. The BIOS is stored on non-volatile memory so I'm not sure why you were having such an issue with it. Hopefully I'll remember this for the future though, just in case!
Bad 💀 Motha Apr 25, 2015 @ 4:13pm 
Dead CMOS battery will rarely do this anyways. The worse that usually will occur is the BIOS not saving your settings once your main power has been disconnected (like pulling the main power cable for a certain period, or turning off your system via a Power Center / Strip, etc.) as without a CMOS battery to keep the BIOS data alive, then it won't keep them saved.

If your system is having Boot related issues, chances are it's probably a faulty Motherboard or other main hardware and not the battery.
Fly Guy Apr 25, 2015 @ 4:17pm 
Originally posted by Bad-Motha:
If your system is having Boot related issues, chances are it's probably a faulty Motherboard or other main hardware and not the battery.

Fortunately, as I already explained, it hasn't been for me. CMOS battery was the culprit. Don't ask me how but after replacing the battery I haven't ran into booting issues or the inability to turn on the computer again.
Last edited by Fly Guy; Apr 25, 2015 @ 5:00pm
Bad 💀 Motha Apr 25, 2015 @ 4:26pm 
Didn't it ever display an error msg at bootup about CMOS Battery Voltage Low? Or something similar?
Fly Guy Apr 25, 2015 @ 4:34pm 
Originally posted by Bad-Motha:
Didn't it ever display an error msg at bootup about CMOS Battery Voltage Low? Or something similar?

Never. The few times I removed CMOS battery it went into BIOS when I turn on the computer. I then just update time and date, save and restart.

Before I had replaced the CMOS battery, whenever I turned on the computer, it would power up for 1.2 seconds and then power off. Then I would have to unplug the PSU and let it sit for hours and only then could I turn in on again, or, it would power off immediately after 1. 2 seconds.

The method that made the computer boot again was to remove the CMOS battery and reinserted it and then wait an hour or more. After that the computer would boot and go into BIOS, but without replacing the weak CMOS battery with a fresh one it occurred again the next morning. The computer powered off after pressing the power button.

Replacing the old CMOS battery with a new one fixed the problem. It does sound odd since most people on the web will asume the problem is a dyring PSU, fried MOBO, CPU or RAM. Fortunately I didn't have to jump through the hoops and purchase unnecessary hardware when the problem was simply a weak CMOS battery.

Last edited by Fly Guy; Apr 25, 2015 @ 5:02pm
Fly Guy Apr 25, 2015 @ 5:05pm 
Here' a comment another person with the exact issue replied:

"I was this close of sending my Corsair 850W to get it replaced. I was having the exact same issues as you've mentioned above. I've done everything: messing with the RAM sticks, changing GPU from one slot to another, re-routing the entire PC cables and updating BIOS.

I've noticed that If I remove the CMOS battery on the motherboard the computer would not start. It didn't make any sense because the battery is only supposed to keep the BIOS data when the computer is turned off. The computer should have booted but it didn't.

I've bought a brand new battery and replaced the dying one. The computer now works like charm. All of the issues I've had before were all fixed. I suggest that you replace the CMOS battery with a new one."
Last edited by Fly Guy; Apr 25, 2015 @ 5:15pm
The Giving One Apr 25, 2015 @ 6:46pm 
Could it be possible that something is constantly causing a draw on the battery circuit and therefore draining it slowly over time until dead ?

That is of course going on what you posted as being the cause and fix.

I have personally never had an issue with one myself, but I am sure at some point in time one needs to be replaced.
Fly Guy Apr 25, 2015 @ 7:03pm 
The battery isn't dead. I never lost time and date. I don't know, but I'm not the only one where replacing the CMOS battery fixed the issue. Hopefully some expert drops along and gives some possible explainations.
Last edited by Fly Guy; Apr 25, 2015 @ 7:04pm
The Giving One Apr 25, 2015 @ 7:11pm 
Sorry then as my choice of words seems to have been inproper. A weak battery then instead of a dead battery. I was just throwing out an idea to think about because those batteries seem to usually last forever in my experience. So that is why I was just wondering if something could be causing a draw on it very slowly over time you see.

For example, cionsidering what we know about the power button on a case and what you posted, it could be possible that there was a very weak connection/corrupt circuit concerning the button or switch in the case. You did suggest that the power button acts strangely sometimes concerning booting up your PC and shutdowns also. Just a thought....
Fly Guy Apr 25, 2015 @ 7:16pm 
Originally posted by The Giving One:
You did suggest that the power button acts strangely sometimes concerning booting up your PC and shutdowns also. Just a thought....

My guess and I don't know anything about computers is that the BIOS data wasn't retained due to weaken CMOS battery so the MOBO didn't give the okay to PSU to go full throttle to boot the computer; it's some sort of protection mechanism.
Last edited by Fly Guy; Apr 25, 2015 @ 7:17pm
The Giving One Apr 25, 2015 @ 7:22pm 
Originally posted by Genghis Khan:
Originally posted by The Giving One:
You did suggest that the power button acts strangely sometimes concerning booting up your PC and shutdowns also. Just a thought....

My guess and I don't know anything about computers is that the BIOS data wasn't retained due to weaken CMOS battery so the MOBO didn't give the okay to PSU to go full throttle to boot the computer; it's some sort of protection mechanism.

I respectfully disagree. That data is stored in a special place. Your custom settings are only lost in the case of a weak or dead or removed battery. The default BIOS settings are input in those cases anyway.
Fly Guy Apr 25, 2015 @ 7:24pm 
Originally posted by The Giving One:
Originally posted by Genghis Khan:

My guess and I don't know anything about computers is that the BIOS data wasn't retained due to weaken CMOS battery so the MOBO didn't give the okay to PSU to go full throttle to boot the computer; it's some sort of protection mechanism.

I respectfully disagree. That data is stored in a special place. Your custom settings are only lost in the case of a weak or dead or removed battery. The default BIOS settings are input in those cases anyway.

I'm just a gamer so it was a wild guess:)

Perhaps they installed a poor battery on the MOBO. I don't really know. I'm just glad that I didn't listen to all the common advice to buy a new PSU, CPU, RAM, or MOBO. Some people have done so and it didn't solve their problem. I'm just very fortunate.
Last edited by Fly Guy; Apr 25, 2015 @ 7:27pm
The Giving One Apr 25, 2015 @ 7:28pm 
Like others here said, this is very strange indeed because a weak battery SHOULD not cause this, but in any case, time will tell for you I am sure...LOL...

Good luck always and thanks for the information here in this thread also...anything newly learned in the PC world is knowledge worth having.
Fly Guy Apr 25, 2015 @ 7:33pm 
Originally posted by The Giving One:
Like others here said, this is very strange indeed because a weak battery SHOULD not cause this, but in any case, time will tell for you I am sure...LOL...

Good luck always and thanks for the information here in this thread also...anything newly learned in the PC world is knowledge worth having.

It is rare case. Read post #6; he's another person I quoted with the same problem with the same fix.
The Giving One Apr 25, 2015 @ 7:36pm 
Oh I believe you certainly and I did see that case already you posted about. Again, thanks for all the info.
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