Holding power button with no power resets CMOS?

A Silver · January 4, 2020

This has happened twice now but I keep forgetting to ask about it.

(detailed story in the spoiler) Long story short when I turn off the PSU or the mains going to my PC and hold the power button, CMOS gets reset. Is that normal?

Spoiler

I went on holiday and turned off the mains plug going in to my PC and held the power button for 10 seconds to discharge any excess power while I was away and when I got home it refused to boot (as it was trying to boot from my old hard drive) and it appeared CMOS had been reset but at the time I had no idea what caused it. A second time I was cleaning the dust out and did the same process, turned the PSU off and held the power button to discharge any excess power while cleaning the components but when I powered the system on, the same message that comes up when you clear CMOS appeared.

Eigenvektor · January 4, 2020

Sounds more like your CMOS battery is dead. So long as you don't unplug your computer you probably don't notice it, but it resets once it has no external power. You could simply unplug it for a minute without "draining" and see if it also resets the CMOS.

A Silver · January 4, 2020

2 minutes ago, Eigenvektor said:

Sounds more like your CMOS battery is dead. So long as you don't unplug your computer you probably don't notice it, but it resets once it has no external power. You could simply unplug it for a minute without "draining" and see if it also resets the CMOS.

That does sound likely. I will give that a go and replace the battery if that is the case.

A Silver · January 5, 2020

23 hours ago, Eigenvektor said:

So I have since tried that and nothing happened. Do you think it is still worth replacing the battery regardless?

Eigenvektor · January 5, 2020

17 minutes ago, A Silver said:

So I have since tried that and nothing happened. Do you think it is still worth replacing the battery regardless?

Good question. If that's not the case, I don't know. On the other hand a battery shouldn't be that expensive? I recently had to replace the one on my mother's board because her CMOS would reset every shutdown. I think we payed about 3-5€ for a double-pack (CR 2032).

Maybe the battery isn't "dead" so much as close to dead so it can still hold on for quite some time before data is lost (just guessing here). You'd probably have to remove it and use a battery tester to check.