PC clock is fast when CMOS battery is low

This is the first hardware issue I write about. That’s normally not the kind of things I’m concerned with. One of my computers (from 2009) showed a strange effect some days ago. I recognised that the PC clock was fast although the time should have been taken from a time server via ntp. Overnight, it was up to 24 hours ahead.

So I examined the whole thing. All I found on the internet said that a PC clock may be slow in case the CMOS battery is low. As my computer in question was antique, I wondered if maybe the battery nevertheless caused the problem. I tried it out and it really worked. With a fresh battery everything was fine again.

In my eyes, this is a remarkable effect and the solution surprised me a little bit. There is no post on this on the internet as far as I know. So I think it was worth to drop some lines here.