acpi alarm not working randomly

[Green_Star]

I am using acpi wakeup alarm to start my machine every morning and evening. It is working some times, not working some times. When ever it didn't wakeup I manually start the machine and see what time the alarm set to. For example if I setup for 2009-08-08 14:15:00, after I booting up it shows as

$ uname -r
2.6.24-24-generic

cat /proc/acpi/alarm
2009-00-00 14:15:00

Like above it is missing the month and date (I checked it before I am shutting down the machine, that time alarm time was fine), so what would be the reason? Mother board battery? Or some other.

Thanks in advance.

[Green_Star]

Is this will CMOS battery problem? Do I need to change the battery? How can I know my battery is low?