Warning: system battery is low.

[Vixen]

I have started getting a "Warning: system battery is low." message on my old Win XP computer when I switch on. I use this machine for all my CAD CAM drawing and photo storage so I need to fix the problem.

I believe the 'system battery' refers to the silver coin size battery in the mother board. I understand it's purpose is to power the EPROM which is used during start up (BIOS) to tell the computer what to do next. Currently, I can press F1 to continue, but even that wont last forever.

My question is how to safely change the system battery. I believe the BIOS information will be lost if I simply pull out and replace the battery. That would be a disaster. Do any of you have experience of replacing the system battery safely.

Mike

[Roger B]

I suggest that you try and find a manual for your computer (online?). There are various ways this can be done.

[gipetto]

win xp is sufficiently modern that there's little useful information stored in the bios. the defaults will most likely work just fine. if you're concerned, then you can enter the bios by pressing delete at the appropriate time, or whatever key it suggests. then you can go through all the headings, noting down the information for each. you will find that most are set to automatic, meaning that they are the default setting. if everything is automatic, you don't need to write anything down.

the most important of these will be the primary and secondary hard disk, if the order is wrong and you have a second hdd, then it will not boot until you enter the bios and change the boot order.
If you have ever swapped ram in the computer, sometimes there are manual timings that should be noted.

[Jo]

Buy yourself a new CMOS battery ... 



If you are worried about doing this then start by making a note of the BIOS Version/Date (its somewhere under the system information screen in Windows if not visible in the BIOS) . Then you can go to the make's website and make sure it is up to date and find out how to load a replacement if required.

Next: Reboot and enter the BIOS and clear the system event log (under the Advanced tab).


With everything powered off, remove the old battery. Leave it out for 10 mins before putting the replacement in position. Put back together and it should boot.

(Its just like being back at work      )

Jo

[crueby]

(Its just like being back at work  )

Jo

Aaaaahhhh! Jo said the 'W' word!!   

[Vixen]

With everything powered off, remove the old battery. Leave it out for 10 mins before putting the replacement in position. Put back together and it should boot.

Jo

Thank you all for your help and guidance. I still feel uncomfortable about pulling the battery in case it wont restart correctly ever again.

Jo  what is the "leave it out for 10 mins" all about? what happens inside that time?

Mike

[Vixen]

Buy yourself a new CMOS battery ... 

Jo

Hello Jo, what happens if I leave the old battery in place? Can I keep pressing "F1 to continue" indefinitely?

Mike

[internal_fire]

The BIOS is stored in EPROM or EEPROM. It does not need any power whatsoever to maintain its integrity. It does need power, of course, to be read during startup and operation, but that is supplied by the mains.

The CMOS battery powers only the parameter storage volatile RAM. The time and date are the most obvious, but as noted above any changes you have made to the defaults in the BIOS are also stored in the volatile RAM.

If you have done little custom modification to your computer (which I suspect) about the only things the CMOS battery and volatile RAM will affect are the time and date.

Gene

[crueby]

Or just convert to steam/mechanical power...

[Jo]

An EPROM has to be given a suntan (Ultraviolet light) to erase its memory (the default BIOS may be an EPROM but more likely to be a "hard written" chip). EEPROMs use a voltage to erase its memory thus we know computers contain some type of EEPROM. The disadvantage of EEPROMS is that their data retention time is not as good as EPROMs (max around 10 years). Muddling the waters: old fashioned EEPROMs required a higher voltage to erase the device, whereas modern Flash memory erases using the standard PC voltage (its the same but different  )

The CMOS battery maintains the modified BIOS values in the EEPROM/Flash as well as powering the clock, when the battery fails the computer will revert to its default BIOS settings e.g. it will start trying to boot off the a: drive etc. and the operating system may well find the clock time a bit of a problem.

The leave it for 10 mins is to let any residual inductance/capacitance discharge in the system which could make the board not recognise the new battery - shouldn't be any but play safe.

Edit: Best write down your BIOS settings first (or take a photo with your mobile phone  )

Jo

[Vixen]

Thank you all for your help and advice, I feel a bit more comfortable now

As far as I can tell, the boot sequence is floppy first then the SATA hard drive, then the SATA CD-ROM.

All the settings appear to be set to factory default:    except:

SATA should be set to ATA, the factory default is AHCI   
Speed Step should be set to ON the factory default is OFF  (whatever that all means)

Does that sound about right???????

I think Chris's steam punk solution is the best

Thanks again

Mike

[Kim]

All sounds quite reasonable.

Speed Step should be set to ON the factory default is OFF  (whatever that all means)

Speed Step is the ability for the BIOS to ramp up and down the clock speed of the CPUs based on actual processing demands.  It is a good thing because not only does it give you more processing power when you need it, it allows the CPUs to cool down when there is less demand. And it saves energy.  Though, the cooling is probably the biggest benefit. Cooler CPUs last longer.  Running them hotter decreases the life of the CPU.

So Speed Step On is the right setting.

Kim

[Vixen]

Thank you Kim,

I had this happen on an identical PC a couple of years ago. Because I did not know any better at the time, so I simply replaced the battery. That PC never worked again and got chucked out.  Once bitten; twice shy. I did not want to repeat history. So forgive me if we go round in circles a few times.

It would appear that changing the battery resets the BIOS to factory default settings, which you should expect to work. However, it appears that this particular model of PC (or Win XP) requires the hard drives to be set to ATA mode rather than the factory default AHCI mode. I guess, not making that change in the BIOS was what killed stopped the previous PC from starting up correctly.
Am I correct in that assumption? even if I do not understand what it all means.

I am still nervous about messing about with my PC. It's like entering the dark side, all mumbo jumbo and occult rituals; known only to a few and understood by even fewer.

Mike

[internal_fire]

Am I correct in that assumption?

It is pretty unlikely that an incorrect setting in the BIOS physically killed anything. There is no way to suddenly apply too much voltage to a component, for example.

The BIOS does not need very much to start up. Only a display and some input device (keyboard, mouse) are all that is required. Incorrect parameters can be then be corrected.

It is possible that some component was already failing, but it was probably not related to the BIOS settings or the CMOS battery.

It is possible that the operating system was affected in some manner with no obvious method of correcting.

Gene

[Krypto]

I use this machine for all my CAD CAM drawing and photo storage so I need to fix the problem.
...

This might be a good time to ask if you have those irreplaceable drawings and photos backed-up on another device?