This Old CMOS Battery

I suppose that if you only keep a PC for a couple of years, you never have to even think about the battery on the motherboard that keeps the CMOS settings saved when you have it turned off.

But if you have an old PC, those batteries will go dead.

On This Old PC, the clock speed was very slow. It would lose whole days of time, not just minutes or hours.

I pulled the cover and found the battery, a typical button cell. I actually had a replacement in the drawer — who knows how long that had been there — and reinstalled. First of all, those batteries are a whole lot easier to get out than to get it, but I did manage to do it.

Did I forget to write down my CMOS settings, which I lost when pulling the battery?


It booted anyway — somehow this BIOS can deal with the hard drives from scratch. The CMOS on this computer was pretty complicated — there are pages and pages of settings. I tweaked something having to do with the sound card, and everything worked fine.

But the PC kept losing time. Perhaps my replacement battery, old as it is, was too dead to use. Bruce suggested that the crystal in the time clock was bad, but I find that very hard to believe. A crystal is a hunk of rock — what could go wrong?

And the thing went totally dead — my clock went back to 1998 the last time I turned it on. I had to hit F1 to complete the booting process, but without doing any CMOS tweaking, it’s running fine.

Still, I’ll have to remember to get a new battery from Fry’s or Target. At least a $3 battery will do it. The PRAM batteries in Macs can run into some serious money, I’ve learned, and it’s refreshing to be able to get the PC battery at any reasonably equipped drug store.