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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2 Answers

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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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:

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:

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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