What are CMOS or Clock Batteries?

CMOS Batteries, Clock Backup batteries, and RTC Batteries perform the same function in desktop and laptop computers: when the computer is turned off, the battery maintains the time, date and information such as the hard drive type, the condition or state of the laptop such as if its on sleep mode, thus insuring their accuracy when the system is once again restarted. These batteries are known alternatively as CMOS batteries, Real Time Clock (RTC) batteries, Bios Batteries or simply internal batteries.

The most common CMOS battery chemistries are Lithium, Nickel Cadmium (NiCad) and alkaline. They are usually somewhere in the 3 to 7.2 volt range and either solder onto the motherboard or plug in via a snap-in connector (depending upon the computer manufacturers design).

In most cases, replacement of the CMOS battery is an easy task. It is simply a matter of locating the battery on the computer's motherboard, removing it and plugging in a new one. As a rule, internal batteries should be replaced by the same type of battery which was originally used in the machine or according to the manufacturers specifications.

The batteries on some Laptops can last from 1 year to 5 years. Some of the symptoms that you will get if your CMOS battery does not work properly are:

You have to set up the time and the date on your machine often

Sometimes the Bios does not recognize the Hard drive

When the laptop goes to "Sleep" it does not recover to the correct state

If you leave a Sony laptop on storage for an extended period of time when you try to start nothing happens

When you turn on the machine you get an error similar to "163 Date and Time Error" or "Error 163"

You get "checksum error CMOS on booting"

You get a message like "RTC has failed the BIOS test"

Also known as RTC Battery, Real Time Clock Battery, CMOS Battery, BIOS Battery, BATTERY BACKUP, STANDBY BATTERY, Nickel Hydrogen battery, CMOS / RTC, BATTERY STORAGE NICKEL, BATTERY NI-MH