The average life of the CMOS battery is around five years depending upon the usage . The CMOS battery needs to be replaced when it is exhausted.
The CMOS memory stores the BI OS settings, boot order , current date, time and other data used during the system booting process.
When the CMOS memory fails due to any technical issues , the BI OS does not get the data required during the booting process. In such cases the booting fails flashing an error message.
However , the most common cause of this problem is the CMOS battery failure. But if battery is good then other causes need to be examined.
When CMOS battery fails , the computer system may experience following problems :