Symptoms
- Computer's date and time reset to a default every time it's powered off
- BIOS settings (like boot order) revert to defaults repeatedly
- A 'CMOS checksum error' or similar message appears at startup
- PC is several years old and hasn't had this battery replaced
Likely causes
- CommonCR2032 coin cell battery has run out after years of useThese batteries typically last several years and are expected to eventually die.
- PossibleBattery contact is loose or corrodedA poor connection can mimic a dead battery even if it still has charge.
- Less commonMotherboard issue unrelated to the battery itselfLess common, but worth considering if a fresh battery doesn't fix the symptoms.
What to do
- Power off and fully unplug the PC before opening the case.
- Locate the small, round coin cell battery on the motherboard, often silver and labeled CR2032.
- Note or photograph current BIOS settings if you've customized any, since they'll need to be re-entered.
- Gently remove the old battery, noting its orientation, and insert a new CR2032 battery the same way.
- Close the case, power on, and enter BIOS to reset the date, time, and any custom settings.
- If the issue returns quickly even with a new battery, check the battery holder's contacts for corrosion or a loose fit.
Tools and parts
- Small flathead screwdriver (optional, to help remove the battery)
CR2032 coin cell batterySearch: “CR2032 3V lithium battery”
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.