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 
IBM ThinkPad R Series -- R40, R40e, R50, R50e, R50p, R51, R52 
IBM ThinkPad X Series -- X30, X31, X32 
IBM xSeries -- 300, 400

IBM P/N: 02K6541, 02K7087, 02K7075, 08K8050, 08K8216,FRU-02K6572, 92P0991, 92P0986 


Package : 1 pcs of CMOS battery