Failing CMOS motherboard battery

The CMOS (Complementary Metal-Oxide-Semiconductor) battery, often an overlooked component, plays a crucial role in maintaining your computer’s BIOS settings. When this small, coin-shaped battery goes bad, it can lead to various issues.

Signs of a Bad CMOS Battery

We asked our Technical Director Michael Jones about how to identify a failing CMOS battery on your motherboard.

  • Incorrect System Time and Date: One of the most common indicators is the system clock losing time or resetting to a default date after the computer is powered off. The CMOS battery powers the Real-Time Clock (RTC) which keeps track of the date and time.
  • BIOS Settings Reset: You may notice that BIOS settings revert to default. This includes boot order, hardware configuration, and system performance settings, which can lead to boot problems or hardware not being recognized properly.
  • Error Messages at Startup: A failing CMOS battery often triggers error messages such as "CMOS Checksum Error," "CMOS Read Error," or "CMOS Battery Failure" during the boot process.
  • System Boot Issues: Difficulty in booting up the computer or an inability to detect drives and other peripherals can also point to a failing CMOS battery.

Solutions and Replacement

Replacing the CMOS battery is a straightforward task. Typically, motherboards use a CR2032 lithium coin cell battery. Here’s a simple guide:

  • Power Down: Ensure the computer is turned off and unplugged.
  • Open the Case: Remove the side panel of your computer case to access the motherboard.
  • Locate the Battery: Find the CMOS battery, usually near the centre or edge of the motherboard.
  • Replace the Battery: Gently pry out the old battery and replace it with a new CR2032 battery, ensuring the orientation matches the original.

Michael says

"To extend the life of your CMOS battery, keep your computer plugged in even when not in use. This provides a small charge that can help maintain the battery’s lifespan. Regularly check your system time and BIOS settings to catch early signs of battery failure. Addressing a failing CMOS battery promptly ensures your system runs smoothly, maintaining your BIOS settings and preventing potential data loss or hardware issues.".

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Michael Jones Data Recovery Specialists   
Michael Jones, Technical Director


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