My system clock slows down if I shutdown system. is it b'coz of my cmos battery is being low?

How do I find whether my system has a cmos battery?How will I know what type, who is the maker etc? How do I know whether it is getting low?can u suggest some softwares that check it? I am rather naive with hardware and has opened the motherboard only to clean it.My PC is 4 yrs old. Is there any problem if I don%26#039;t change it other than system clock becoming low.If it is necessary to change cmos battery how much does it cost in rupees?|||I believe most CMOS batteries are 2032 batteries. You should be able to find them anywhere and they aren%26#039;t really machine specific. I%26#039;m not sure about laptops though.|||Replace the battery. Your motherboard is unable to retain the information because the battery is dying.