LinuxQuestions.org - [SOLVED] A way to know if the CMOS battery is installed without opening the case?

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- - A way to know if the CMOS battery is installed without opening the case? (https://www.linuxquestions.org/questions/linux-hardware-18/a-way-to-know-if-the-cmos-battery-is-installed-without-opening-the-case-4175464337/)

A way to know if the CMOS battery is installed without opening the case?

Hi: that is, the machine case. To see by myself I changed the BIOS settings to some arbitrary values, turned off the machine, then turned it on. And the new values persisted. Can I safely infer that the battery is there?

if the new settings persisted, then it's a fair bet, that the battery is intact ..
- if it was not, - you would lose those settings, when the PC is left for a while, with no power.

Another way to tell is that the battery is needed to keep the clock running so if you're not using ntp and your clock shows the right time after the machine has been switched off for a while the battery must be there.

Yes, it's some minutes now since I turned it off. I'll see now what happened. If the time is OK, the I shall have to open it, because some files are being listed with incredible times.

Still worried about cracking open the case? Its quite often the fastest and easiest method.....

Even if the CMOS battery is dead/missing, if you leave the power supply plugged in the system can keep its settings. The only way to know if the CMOS battery is dead/missing without opening the case is to turn the machine off then unplug the power supply.

Quote:

Originally Posted by cascade9 (Post 4963421)

I'd forgotten about this. As you say the easiest way is simply to open the case.

Hi,

Add to what cascade9 has stated; once system is unplugged it may take some time lapse for the decay therefore without shorting the CMOS shorting jumper it may take a while before BIOS reverts/changes state.

Quote:

Originally Posted by onebuck (Post 4963444)

Presumably the clock will stop ticking fairly soon after the power is taken away though?

Quote:

Originally Posted by cascade9 (Post 4963421)

So it's not enough to press the power on/off switch. You must unplug the power cord! So pressing the switch to turn it off the machine is still draining current from the mains! Well, if you can turn on the machine only by pressing a soft touch button then some part of the machine has to remain energized. Oh happy times when you just lifted a lever and all power to tha machine was off!

Quote:

From onebuck:
Add to what cascade9 has stated; once system is unplugged it may take some time lapse for the decay therefore without shorting the CMOS shorting jumper it may take a while before BIOS reverts/changes state.

I had been thinking about that. But did not know the power supply remained on.
__________________

Hi,

Quote:

Originally Posted by stf92 (Post 4963465)

Quote:

excerpt from CMOS Battery;
The memory and real-time clock are generally powered by a CR2032 lithium coin cell. These cells last two to ten years, depending on the type of motherboard, ambient temperature and the length of time that the system is powered off, while other common cell types can last significantly longer or shorter periods, such as the CR2016 which will generally last about 40% less than CR2032. Higher temperatures and longer power-off time will shorten cell life. When replacing the cell, the system time and CMOS BIOS settings may revert to default values. This may be avoided by replacing the cell with the power supply master switch on. On ATX motherboards, this will supply 5V power to the motherboard even if it is apparently "switched off", and keep the CMOS memory energized. In general one should not work on a computer that is powered.
Some computer designs have used non-button cell batteries, such as the cylindrical "1/2 AA" used in the Power Mac G4 as well as some older IBM PC compatibles, or a 3-cell NiCd CMOS battery that looks like a "barrel" (common in Amigas and older IBM PC compatibles), which serves the same purpose.

Please note the ATX reference above. :)

Well, you've finally made to open the case. The battery is certainly there. If it is dead or not is another matter.

EDIT: sorry. I did not refresh the screen and didn't see your post, onebuck. Thanks for the reference, though I already knew the article.

Can a pc even boot without one?

Yes most systems can boot without a CMOS battery Habitual. I dotn think I've run acrross a x86 system that wont boot without a CMOS battery, but I dont go around remvoing them to check ;)

Quote:

Originally Posted by onebuck (Post 4963470)

Please note the ATX reference above. :)

I should have said 'ATX only' in my post, but I figured that the last AT systems I saw had P2/Celeron CPUs, and I havent seen any new AT systems since 1999/2000 or so.

I've come across a few systems with dead CMOS batteries that have booted and a more recent machine (from between 5 and 10 years ago) that complained in its POST that the battery was low but still booted.

Hi,

Quote:

Originally Posted by cascade9 (Post 4965809)

Yes most systems can boot without a CMOS battery Habitual. I dotn think I've run acrross a x86 system that wont boot without a CMOS battery, but I dont go around remvoing them to check ;)

I should have said 'ATX only' in my post, but I figured that the last AT systems I saw had P2/Celeron CPUs, and I havent seen any new AT systems since 1999/2000 or so.

I added the info to clarify things to the thread.

Just small footprint motherboards/SBC. If the BIOS itself is faulty then booting could be an issue.Usually BIOS does default to original state so a boot would be possible if the storage media is default boot device once power is applied.

I once experimented by removing power from motherboard and waited a few days to see if the BIOS settings changed. Machine booted with original settings so decay would depend on the capacitor retention and battery condition. I usually replace the battery if it's possible issue since the cost is minimal and not worth wasting time. Purchase the batteries in lots so the cost to clients is minimal.