I recently encountered random then more frequent POST problems with my 2 yo mother board. The internal clock was OK so at first I did not look at the CMOS battery and as I

The CMOS battery in my Windows 98 machine is still going strong. It is unplugged now most of the time. You could have a dud, but it's rare. The first thing I do if I suspect any battery is to take it out and put it back in. Sometimes reinstalling it cleans the connection. Bob

In my experience these batteries last about 5-6 years but yes, they are only used when the PC is disconnected from a power source.When the PC is off but still connected, the batteries are not used. Off course over time every battery loses it's power slowly.I manage over 400 PC's and very rarely I had to replace batteries. Even PC's that are over 6 years old rarely have this problem but I noticed that in all cases those PC's were disconnected from a power source when not in use. Once I had a bad batch that needed it's batteries replaced on a yearly basis but that was over 12 years ago (a rare breed of Apple Mac's)Allard.