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UPDATE: While I think I might still have a "dead" CMOS battery, the main cause of the problem behaviors turned out to be CPU temps. One hex nut in the backing plate of the CPU cooler had come out, causing one of the 4 posts of the CPU cooler to not screw down, resulting in extremely high CPU temps (70 degrees c at idle). Pulling out the mobo and fixing this problem has brought CPU temps instantly down to where they should've been and I now believe the machine will be stable once more (still gonna try a fresh CMOS battery though).

UPDATE 2: Ordered a brand new battery, but CMOS settings are still lost on removing power even though everything else about the machine is now stable. Very odd.

My 8-9 year old Windows desktop has been acting really crazy the last couple of days, random shutdowns, refusals to boot/POST (and no beep codes), and most consistently, loss of CMOS settings on every cold boot (a boot after having removed all power).

So this sounds like a very straight-forward dead CMOS battery. But I tested with a voltmeter and the battery reads just over 2.9 volts, which seems like it should be plenty. I swapped it with another battery (and the only other one I have laying around) and it's also about 2.9 volts, no change in behavior.

Settings are not lost if I do a warm restart, or even a full shutdown without removing AC. I could order a replacement battery but this just seems so unlikely to me, but I can't find anything specific about CMOS voltages other than about clearly dead batteries.

Is 2.9 volts really low enough to cause loss of CMOS settings?

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    That is within a tenth of a volt of new and so I do not think this is your issue. Run the computer manufacturer's hardware tests to see if other hardware issues are pinpointed – John Apr 13 '20 at 1:58
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    Find the motherboard, disk, and memory test applications. I think it is like a motherboard issue at this point – John Apr 13 '20 at 2:04
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    Do you have another keyboard laying around? You could disconnect the current keyboard and mouse (an other devices) and just use the new keyboard (no mouse necessary). You turn it on, change the date, turn it off and back on and see if it sticks. A short in the USB cables for example could trigger all sorts of weird behaviours and could happen just by moving the mouse/keyboard around. Worth a try. – Eduardo Trápani Apr 13 '20 at 2:13
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    Take the radio usb thingie off too (the one for the wireless mouse). It's better to suspect everything. And, I guess you have tried, but if there is something like a dip switch near the CMOS battery, check the manual and reseat it. – Eduardo Trápani Apr 13 '20 at 2:16
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    As uncool as it sounds - could you do a visual inspection of the motherboard and check for corrosion or other damage? Also try cleaning the terminals of the battery holder with a regular erase or magic eraser (its a soft malamine foam) in case its oxidised. – Aibobot Apr 13 '20 at 2:31
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My experience with computers goes back a long way. When they malfunction at 7 years or beyond, I generally replace them. Me and my clients as well. So that is the suggestion I make to you here - replace.

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  • Thanks. I actually ordered a replacement machine about 2 hours ago, but while I'm waiting for it to arrive I'm still trying to figure out what's actually wrong with this one, either so I can end up with a spare lower-end machine, or so I can keep the components that are in fine working order in case I can use them down the road. The troubleshooter in me is super annoyed to not be able to figure this one out! – JVC Apr 13 '20 at 2:13
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    Thanks for the update and good luck – John Apr 13 '20 at 2:22
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I am not sure this is being answered that nicely.

Nominal voltage of batteries like CR2032 is 3 volts, but the real measured voltage is normally over 3 volts.
I just tested a fairly new functional battery and was 3.4 volts.

Some Motherboards are very sensitive and 2.9 might be enough to make them fail.

Voltage is Not the only factor in terms of the battery being usable, the milliamps that the battery yields are also important. See video below: https://www.youtube.com/watch?v=CZ3PwVtCe1A&vl=en

Other completely different issue could be the possibility of degradation up to the point of failure in Motherboard components, that could cause that now they need a bit more power. Below from Wikipedia(at times considered unreliable) but is a known fact: https://en.wikipedia.org/wiki/Failure_of_electronic_components

Some of us old technicians have plenty of experiences with some Electrolytic capacitor degradation years ago that they starting loosing their values and they cause different issues in the Motherboards, at times reflected in the computer behavior.

Also with time a small layer of dust could be on top of the components and accelerate or the mentioned degradation or cause some other issues.

With that said a good recommendation(if you are interested in keeping a computer that is already 8-9 years old), is to thoroughly clean that Motherboard(there's plenty of how to recommendations in the internet) and later replace that battery.

If the battery is hard to find or don't have a replacement you can temporarily set other small battery that have at least over 3 volts(or a couple of small 1.5v in series), but try not to go over 3.5v. While most Motherboards have all kinds of capabilities to avoid damage if the voltage is over, is better to be safe that sorry.

I hope this helps,
Ramón

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  • Thanks, for now I've ordered a new machine as the purposes for it are such that it needs to be absolutely reliable (as much as a computer can be anyway). But at some point I may get ahold of a brand new battery just to completely rule that possibility in or out. – JVC Apr 13 '20 at 21:01
  • Two different batteries were tried so it is more likely to be the board as we surmised earlier. – John Apr 14 '20 at 10:28
  • FYI, the major problems I was having turned out to be CPU cooler related. See my update if you want the details. – JVC Apr 14 '20 at 15:22
  • Yes, read the update and up-vote this inquire. Great to read that you rule-out your main problem. Noticed that a mechanical disconnection caused the heat problems. Any failure can cause other components to fail, including what seems this time the batteries. Be aware if other batteries keep failing could be that some other components are bad. Best regards – Ramon Maldio Apr 16 '20 at 0:43
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    Interestingly there were definitely two, separate issues here. The heat issue was responsible for the erratic behavior, random crashes, etc. Machine is perfectly stable now, except that the CMOS is still lost on removing power, even after putting in a brand new battery (tested at about 3.3volts). So I don't know what's going on but I'm still relegating this machine to the role of spare. – JVC Apr 20 '20 at 22:08

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