Different BIOS can give an error in different ways, here are a few options:
CMOS Battery Low
CMOS battery failed
State Battery CMOS Low
CMOS Battery Has Failed
System battery is dead
CMOS Battery State Low
An error is displayed when the computer is turned on and indicates that the battery needed to store BIOS settings is empty.
The solution is to replace the battery. It is also possible to clean the contacts. To do this, you need to remove the battery from the motherboard, check if there are dust on the contacts, if there is a tester, then measure its voltage, it should usually be no lower than 3 volts.