CMOS battery

[hneaz]

how often should you change it if u use the pc twice a day? i have this emachines for 3.5 years and i think the setup says there is a problem with the battery.

 

[Link]

Don't bother changing it unless your system clock starts losing time.

Give us the message, generally the bios won't detect a failing cmos bat, it might be something else.

 

[Asus]

You might be getting to that time when the battery is going out (3.5yrs). They can go for quite a while though.
Not too hard to find them. I think they are CR2032 3v battery.