What is a CMOS battery?

Core functions of the CMOS battery

Application scenarios and technical differences

Fault symptom diagnosis guide

Professional replacement procedure

CMOS battery vs SSD cache battery comparison

Frequently Asked Questions

A CMOS battery is a coin-type lithium battery (common model: CR2032) with a diameter of about 20mm and a thickness of only 3.2mm. It looks silver-white. According to the 2023 Global Hardware Maintenance Report, 90% of consumer-grade motherboards use a lithium manganese dioxide primary battery (Li-MnO₂ chemistry). Only industrial motherboards or embedded systems may use rechargeable lithium-ion solutions (e.g., ML series).

Deep look at physical features:

• Energy density: Typical capacity is 220mAh (milliamp-hour). It can discharge at 3V for about 73 hours.
• Environmental adaptability: Works from -20℃ to 60℃. It still works in extreme environments.
• Lifetime index: Self-discharge rate ≤1% per year (alkaline battery is about 3-5%). Service life is 3-10 years.
• Structure design: Stainless steel shell + PTFE (polytetrafluoroethylene) sealing ring. It prevents electrolyte leakage and motherboard corrosion.

BIOS/UEFI configuration storage

• Test data: A good battery can keep BIOS settings for up to 1825 days (5 years) without power.
• Data volume: Modern UEFI stores 200+ parameters (300% more than early BIOS). This includes:

• Hardware boot order table
• Secure Boot Keys
• TPM (Trusted Platform Module) security chip settings

Real-Time Clock (RTC) power supply (time accuracy)

• RTC chip power use is only 300nA (nanoampere). Without power, daily time error can be ±2 seconds.
• Data center test: A 5-year-old CMOS battery can cause a 15-minute monthly time error.

Overclock configuration protection (performance)

• It stores memory XMP/DOCP settings and CPU multiplier/voltage parameters.
• Failure result: i9-13900K overclock settings lost may reduce performance by 30%.

Special warnings:

• High-end graphics cards (e.g., RTX4090) VBIOS chips need a separate battery.
• RAID card battery failure can damage cache data.

Main symptoms (87% cases):

• Boot shows "CMOS Battery Failure".
• System time resets to January 1, 2000.

Advanced symptoms (hardware settings lost):

• BIOS returns to default settings (overclock/memory settings lost).
• Device Manager shows unknown PCI device errors.

Hidden risks (need multimeter test):

• Battery voltage <2.5V (normal 3.0-3.3V).
• RTC circuit current on motherboard rises to 50μA+.

Laptop special cases:

• ThinkPad requires removing the keyboard (5 clips).
• MacBook Pro requires disconnecting the touchpad cable.

Test data: Industrial CMOS battery can keep >80% capacity after 300 charge/discharge cycles. Consumer-grade batteries must not be charged.

How to remove cmos battery?

Before removing the CMOS battery, shut down and disconnect the computer's power. Open the case, identify the circular battery (usually a CR2032) on the motherboard. For clip-secured batteries, gently pry it out with a small tool; for socket-mounted types, lift it carefully. Handle the battery with care to prevent damage.

What is cmos battery?

A CMOS battery is a small, coin-shaped lithium cell (often a CR2032) that supplies power to the CMOS chip on a computer's motherboard.

What does the cmos battery do?

A small yet critical component, the CMOS battery powers the Real Time Clock (RTC) and maintains BIOS settings while the computer is powered off.

Where is the cmos battery located?

On desktop motherboards, the CMOS battery is usually found next to the BIOS chip. For laptops, it's commonly situated under the keyboard or beneath the bottom panel. This small, silver, coin-shaped CR2032 cell fits into a clip-on holder or socket.