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 :

Compaq Presario Series

F500, F502, F503, F505, F506, F551, F552, F553, F555, F557, F558, F562, F564, F565, F577 

P/N: 431436-001



Package : 1 pcs of CMOS battery