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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting the Motherboard and System Devices | CMOS Memory or Real-Time Clock ]

The CMOS battery is dead or dying

Explanation: The system is exhibiting behavior that implies that the CMOS battery is dead. This can include lost CMOS settings, the real-time clock losing time, or of course dead battery warnings at boot time.

Diagnosis: On an older PC, it is normal for the CMOS battery to fail at some point in time. They usually last for many years, with over five years being the norm, at least on older machines. Nobody knows for sure how newer machines will fare. On a new motherboard, this sort of message is a sign of a defect, although you shouldn't worry about it if it appears only the very first time the board is powered up. The solution is replacing the battery, and this can be an either easy or impossible task, depending on how much thought the motherboard manufacturer put into the design.


  • If this is a new motherboard and you are getting an error saying that the CMOS memory was cleared, or that the battery is dead, try rebooting the machine and seeing if the message goes away. If it does, then the problem is probably resolved as long as it does not return.
  • If this is a new installation and you are getting the error continuously, I would double-check any jumpers associated with the battery. Some motherboards have a jumper to select between using an internal and external battery. Also, check out these common problems with new installations.
  • Replace the CMOS battery. Note that on some motherboards it is not possible to replace the battery because it is integrated into the motherboard or a component such as the real-time clock. This is a bad design by engineers who lack vision, but is unfortunately all too common these days.
  • If the battery cannot be replaced, or replacing it does not solve the problem, troubleshoot the motherboard.

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