Glossary → Desktop PC Repair Terms
What Is a CMOS Battery?
The small coin battery that keeps your PC’s settings alive.
Definition: The CMOS battery is a small coin cell (usually a CR2032) on the motherboard. It keeps the system clock running and stores BIOS settings while the computer is unplugged. Typically it lasts several years.
Signs the CMOS battery is dying
The date and time reset whenever the PC is unplugged, you see “CMOS checksum error” or “press F1 to continue” at startup, BIOS settings keep reverting, or websites show certificate errors because the clock is wrong.
Desktops vs laptops
In most desktops it’s a simple clip-in battery. In laptops it’s often a wired cell hidden under other parts, so the laptop has to be partly taken apart. Either way it’s an inexpensive part.
A useful reset
Clearing the CMOS restores the BIOS to its default settings. Technicians use it to recover from bad settings that stop a PC from passing POST.
Related terms
→ BIOS — the settings the CMOS battery keeps saved
→ Battery Health — not the same thing: that’s your main battery’s capacity
Clock keeps resetting?
Usually a quick, low-cost fix. Free diagnosis and quote.