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, T40p, T41, T41p

T42, T42p, T43, T43p
T60, T60p, T61, T61p

IBM ThinkPad R Series -- R50, R50e, R50p, R51, R52, R60, R60e,  R61, R61i

IBM ThinkPad X Series -- X30, X31, X32

IBM xSeries -- 300, 400

Lenovo Series -- T400, T500, R400, R500, W500, W700


Package : 1 pcs of CMOS battery