CMOS Battery - Are there any serious implications if it is low on charge

Hi All,

Had a conversation with a customer today, where I noted that the CMOS battery on one of their PCs in the warehouse has a 'low battery' warning on boot up.

It is a Dell and you can press F1 to bypass / acknowledge the warning, and continue to boot up the OS.

I said they should replace the battery or the machine, to which I was asked, 'Why - what are the implications?'

I said that the battery allowed the machine to keep track of time while powered off, to which the customer noted that when the machine boots up it gets it time from or or wherever, so why does it matter.  The machine is not domain joined, so any implications from that are not applicable.

I didn't have a reply!

Is there any implication to just leaving the machine as it is other than having to press F1 after it boots (which does mean if it automatically updates, then it won't reboot into the OS, but will get stuck on 'Press F1').

Also, if there are no significant implications, does anyone know if we can change a setting somewhere (BIOS perhaps) to disable that warning?  I did have a look, but nothing jumped out at me.


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dbruntonConnect With a Mentor Commented:
Generally it is a 5-10 minute job to change the CMOS battery if this is a pretty standard machine.

The implications are if this machine has slightly non-standard settings.  You might have tweaked the BIOS settings for a special setting, for example if you wanted it to boot from the second hard disk instead of the first.  If the battery is flat it would boot from default settings which would probably be the first hard disk.  Yep, you can get around this problem but a full battery would be better.

Also see

Some users experience symptoms with dying or dead batteries.   See for example, so the statement up above may not necessarily apply to all computers.
Tom CieslikConnect With a Mentor IT EngineerCommented:
Not only TIME but all Bios settings like HDD configuration S.M.A.R.T. settings, information about passwords in BIOS, defauld video adapter if is more than one, and all other user settings.

Also if User will boot computer with wrong Date and time some application will not work till computer will synchronize time with DC or Time Server
Mal OsborneConnect With a Mentor Alpha GeekCommented:
The battery powers the real time clock, as well as keeping the BIOS setting live.

If it dies, the machine will pause at boot, not know the time, and forget any setting that have been made in the BIOS. It may still boot OK and eventually sync the time.

Frequently, the CMOS "battery" is a single lithium coin cell, clipped into a holder. Usually a CR 2023. These are readily available for a couple of dollars, and very simple to replace. If it were me, I would be looking at just replacing it.

Here is a writeup with some pictures:
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dbruntonConnect With a Mentor Commented:
>>  Usually a CR 2023.

Er no.  Usually a CR2032.
Dave BaldwinConnect With a Mentor Fixer of ProblemsCommented:
Time is updated from an internet time server periodically but not every day.  Right now this computer is supposed to update again on 11/6/2017.  If the battery dies and the date/time goes back to some much earlier time, the update might not happen for a long time, maybe years, I don't know.

In the mean time things like SSL/TLS certificates that rely on date/time may not be considered valid and they may not be able to surf HTTPS sites.
nobusConnect With a Mentor Commented:
i have seen all kinds of weird things happening with a low battery, ranging from not booting at all, over identifying wrong hardware, or some  - not all, and booting up with all weird kind of problems
so get that battery changed (cos= 1$) - or leave it, but make sure he knows it 's his responsability if anything goes wrong
it is ok for a customer to ask questions, but remember that any fool can ask more Q's than a sage may have answers for...
AlanConsultantAuthor Commented:
Thanks guys - I should have thought about the BIOS settings (although it is most likely that they are all 'factory default' anyway), and I have never (that I know of) seen any of the oddness that you are describing, but I will re-iterate the advice to replace the battery given they are so cheap.

andreasSystem AdminCommented:
ITs better to change. If time wont auto sync and is back to the bios default. SSL in the browser wont work anymore as the certs are invalid for that time. It might go as far as auto updates are not running anymore as update servers cannot be verified.

This is imho, next to the problem that if might not boot, the biggest problem.
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