I'm pretty sure they're all 3 volts. Most Pentium class or later PCs should use the round, clip-in batteries.

But check on the board, just to be sure it's not an older style one, soldered to the board.

I've never really seen those on anything later than a 486 though.

Any electronics store will stock the batteries you need.

As Catweazle said, your best bet is to crack the case and check the model/part # of the battery. Many are the flat, round "watch-style" (CR-2032 or similar), but not all.

http://www.batterypower.net/

Yeah looks like there all really the same.

Tee-hee!

There are so many more but, just typed it in google and got that one I really never needed a CMOS battery maybe once so I just took it out of a old motherboard. Anywho.

Ok, the last time that I checked it was round and silver. So it should be fine. But I see on www.batterypower.net that there are indeed different brands of CMOS battery's. And Catweazle you mean something like this one?
http://www.batterypower.net/Images/C.../CR2430LIL.jpg " Contura 3/20, 3/25, 3/25C, 386 (rtc)"
Code: CR2430-1026

That's the basic shape, yes. You do want to check the actual CRxxxx or whatever part # though, as the diameter of those style of batteries does vary. Also, there's often no need to hunt for the batteries online. Those types are pretty common; I can usually find them at my local drug store or Radio Shack for a couple of $$.

heh heh..

I guess i'm a bit 'rough and ready' in my own appraoch. I'd just grab the old one toddle off to an electronics store or other stockist, and tell 'em i want one same size, same voltage. If it fits it's OK!

The voltage is the crucial thing, because it powers CMOS and clock, and you don't want THOSE buggered up or there's gonna be problems!

Yeah just bring it in some store like RadioShack or something show them the battery and tell them you want a new one. Or just say you want a battery for your CMOS battery for your Motherboard I am sure they will give you the right one. Besides it's only what 2 dollars?