Cause:
Like any battery the computer CMOS battery can fail or lose its charge.

Solution:
If your computer is losing its time or date settings�� or you are receiving a message CMOS Read Error�� CMOS checksum error�� or CMOS Battery Failure�� first try leaving the computer on for 24-hours. In some cases this can charge the battery and resolve your issue. This often resolves CMOS battery related issues when a computer has been left off for several months. 


Compatible with the models :

IBM Thinkpad 570 Series -- 570  570E  570X  570Z 
IBM ThinkPad A Series -- A20  A20P  A20M  A21  A21E  A21M  A21P  A22 A22M  A22P  A23  A30 A30P  A31P 
IBM ThinkPad T Series -- T20  T21  T22  T23  T30  T40   T60 
IBM ThinkPad R Series -- R40  R40e  R50  R50e  R50p  R51  R52  R60 
IBM ThinkPad X Series -- X30  X31  X32 
IBM xSeries -- 300  400 
 
P/N: 02K6541  02K7087  02K7075  08K8050 


Package : 1 pcs of CMOS battery