CMOS / Motherboard Battery Replacement
What the CMOS battery does, which model to buy, and where it hides on your board.
The CMOS battery keeps your BIOS settings and the system clock alive while the PC is off. When the clock resets every boot, the cell is done — a 10-minute replacement.
Power down and unplug
Shut down the PC, unplug the power and hold the power button for 5 seconds to drain residual charge.
Locate the cell
It is a shiny coin cell in a small holder, clearly marked with + polarity.
Release the old cell
Use a small flat tool or thumb to spring the holder — never force, holders are plastic.
Fit the new one
The + side faces the stamped symbol. Power on and re-set the date and time.
Which model should I buy
CR2032 covers roughly 90% of motherboards. Slim notebooks may take a CR2016; a few servers use CR1632 or CR1220. Always read the old cell.
A 3V lithium coin cell sits on every motherboard. While the PC is on, the power supply keeps the settings; when the PC is off, the cell keeps time and the BIOS defaults.
Symptoms of a dead CMOS battery: clock reset on every boot, BIOS settings lost, or a low-battery warning at startup.
FAQ
What happens when the CMOS battery dies?
The clock resets and BIOS settings and boot order are lost on every power-off.
Where is the CMOS battery on my motherboard?
A silver coin cell in a black holder — near the CPU on desktops, under the bottom cover on notebooks.
How often should the CMOS battery be replaced?
Three to five years in a typical desktop; longer if the PC stays plugged in and used.
Which battery does a motherboard use?
CR2032 in most cases — check the stamped number; slim models use CR2016.
Can I replace the Dell / HP / ASUS CMOS battery?
Yes — it is a standard CR2032 coin cell. Match the model and the polarity.