CMOS BIOS battery failure

  • Thread starter PainterGuy
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Summary
battery failure in a CMOS BIOS and restoring the BIOS settings
Hi,

I was reading about CMOS BIOS which was once used in computers to store BIOS settings is a CMOS RAM using a battery backup.

This article, https://www.makeuseof.com/tag/why-does-my-motherboard-have-a-battery/, says, "If the battery fails on an older computer that stores its BIOS settings in CMOS, you’ll see error messages like “CMOS Battery Failure”, “CMOS Read Error”, or “CMOS Checksum Error” when you start the computer. You may also see more cryptic error messages, like “New CPU Installed” – the motherboard can’t remember that the CPU was installed previously, so it thinks it’s new every time you boot your computer."

If the battery fails, it'd mean losing all the BIOS settings which in turn means that a computer hardware would no longer be able to make heads or tails of anything. Unless there is a backup copy of BIOS settings, I don't think replacing a battery would restore the BIOS. But I have been to some other online sources which suggest that replacing a battery would fix the problem. Could you please guide me on this? Thank you!
 
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Replacing the battery will no nothing in and of itself to restore the settings, but how much of the information gets restored as defaults is likely a function of the BIOS itself. Very likely you will have to open the BIOS manager and tell it all over again about your hard drives, for example.

Also, the computer's clock is likely running off of the same battery as the CMOS so you'll have to set the time on the computer as well.
 
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Bios is in static readonly memory no batt needed to keep its defaults. However you must configure your machine and those changes need the battery to be charged to maintain them. There may be a short time where theyll still persist but eventually they will vanish when the battery is completely used up. This aslow you to pop the old batt and pop in a new one.
 

vela

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If the battery fails, it'd mean losing all the BIOS settings which in turn means that a computer hardware would no longer be able to make heads or tails of anything.
If the system is properly designed, it should be able to recover from this kind of situation. Most likely, it will assume a lowest-common-denominator default settings that will allow the system to begin booting, although not optimally, and there should also be a way to reset the settings to these default values manually. You'll have to subsequently reconfigure the settings to tailor them to your hardware.
 

rbelli1

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If the system is properly designed, it should be able to recover from this kind of situation.
Generally this is the case.

There was one Intel chip set (one of the 810 series if I recall) That had to be specifically told to reset corrupted settings. So it would not run without a battery and if the battery died you have to short some pins together and put the new battery in and then press the power button un-short something turn around and do the hokey pokey or something like that.

Most of them will just work at default settings and the only problem is some unusual beeping and you may have to press some key or another to continue.

BoB
 

Vanadium 50

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Most likely, it will assume a lowest-common-denominator default settings that will allow the system to begin booting
Many of the systems of the Bad Old Days would only boot to the BIOS settings, where you would then enter whatever you needed. Good enough, if not exactly good.
 

rbelli1

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Many of the systems of the Bad Old Days would only boot to the BIOS settings, where you would then enter whatever you needed. Good enough, if not exactly good.
Yes. I had forgotten the times before auto HDD detection.

Thanks ever so much for reminding me!

BoB
 
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Thank you, everyone!

Replacing the battery will no nothing in and of itself to restore the settings, but how much of the information gets restored as defaults is likely a function of the BIOS itself. Very likely you will have to open the BIOS manager and tell it all over again about your hard drives, for example.

Also, the computer's clock is likely running off of the same battery as the CMOS so you'll have to set the time on the computer as well.
If the system is properly designed, it should be able to recover from this kind of situation. Most likely, it will assume a lowest-common-denominator default settings that will allow the system to begin booting, although not optimally, and there should also be a way to reset the settings to these default values manually. You'll have to subsequently reconfigure the settings to tailor them to your hardware.
Many of the systems of the Bad Old Days would only boot to the BIOS settings, where you would then enter whatever you needed. Good enough, if not exactly good.
I have boldfaced the important sections in the quotes above.

It looks like in case of battery failure in a CMOS BIOS, the settings could be restored with some extra work on the part of a user. It implies that there was some kind of an additional nonvolatile memory which came into the action after the computer power-on even before the BIOS itself. Actually, such a nonvolatile memory would be a precursor to BIOS memory.

The attached text could be helpful. Thank you for your help and time.
 

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rbelli1

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BIOS memory.
There are actually two parts to what you would call the BIOS memory. There is the non-volatile part that stores the initial boot code and there is the battery backed SRAM part that stores configuration.

The bios will load a default set of configuration on startup if there is no battery backup available. This almost always does not require user intervention.

Some systems will need to be configured before they will work properly. This is not the case with most systems assembled in the last nearly two decades or so. The default settings on most newer systems will work fine and the BIOS will be able to auto-configure the hard drives.

Older systems will have no boot devices configured as default so those will need to be entered. Other configuration will need to be changed for non-default usage. The defaults for older systems for a long time were to be as compatible as possible for the default settings. This required the devices to be set to the enhanced type or usually there was an "Optimal" setting that would changed all devices to be the enhanced mode.

It is rather odd that we still use SRAM to store settings that are often only changed once when a system is built. This was done originally since non-volatile EPROMS required a treatment with UV light to be rewritten. Since the technology has been commonly available for something like 40 years the battery should only need to run the clock.

BoB
 
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Very old computers - I'm recalling an AT clone circa 1985 - didn't have a ROM-based BIOS boot menu. On the one I have in mind, when the CMOS backup battery died, or memory got scrambled in some other fashion it was necessary to boot to a floppy in drive A (disk 0) containing a BIOS setup program, and run it to re-enter HDD parameters, date/time (and perhaps other things - its been too long to recall). This was before HDD auto-detect existed, and it was common practice to write down HDD parameters on a sticky note or 3x5 card Scotch-taped to the chassis to aid in the process.
 
When I started to use one of my first PC there's not CMOS setup at all nor a software to configure it.
You have to do all via switches or jumpers, a very hardware method.
For nostagic like me here can be found a lot of amazing references on that old chaps: minus zero degree (-0°)
 

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