Signs the CMOS battery might need replacing:
- BIOS UI stops responding to keyboard input after a few seconds
- Getting into the BIOS UI is tricky/flaky
- “CMOS checksum error” on boot
Other things I tried that didn’t help:
- Reset the CMOS by shorting the
- Unplug all RAM and try one stick at a time.
- Unplug all hard drives
- Different keyboard/USB port combinations.
Replacing the physical CMOS battery (probably 5+ years old at this point) fixed things completely.