How to tell if your CMOS battery needs replacing

One time, when I booted up my desktop computer, I came across this message, "CMOS Settings Wrong," which prompted me to press either F1 or F2 key. I tapped the key F1, and default values were loaded. I noticed that the date and time in the taskbar was not correct. I rebooted my computer, and this time I encountered the same message again, and tapped F2 key (instead of F1). The BIOS screen appeared, I set the date and time correctly, pressed ENTER, then F10 to save setting.

I searched in the net what was causing this problem. Then, I got to know that it's the CMOS battery that is dead or dying and needs replacing.

I once again rebooted my computer, pressed either F1 or F2, and the date and time synced out again.

One startup to another, the same problem is encountered. The CMOS battery in my desktop computer needs replacing!

CMOS (Complementary Metal-Oxide Semiconductor) is a small amount of memory on the motherboard that contains the BIOS settings. It is powered by CMOS lithium cell, CR2032.

According to Wikipedia: The BIOS software is built into the PC, and is the first code run by a PC when powered on ('boot firmware'). The primary function of the BIOS is to load and start an operating system. When the PC starts up, the first job for the BIOS is to initialize and identify system devices such as the video display card, keyboard and mouse, hard disk, CD/DVD drive and other hardware. The BIOS then locates software held on a peripheral device (designated as a 'boot device'), such as a hard disk or a CD, and loads and executes that software, giving it control of the PC. This process is known as booting, or booting up, which is short for bootstrapping.

The memory and real-time clock are powered by CR2032 lithium cell. Battery is about the size of a coin.

Depending on the type of motherboard and length of time of computer use, CMOS batteries will last from 2-5 years. Longer power-off time, shutting down many times and higher temperatures shorten the battery life.

When CMOS battery is dead or dying, you will encounter any one of these messages in booting up:

• CMOS Settings Wrong
• CMOS Read Error
• CMOS Checksum Error
• CMOS Battery Failure

In my case, I encountered "CMOS Settings Wrong."

• Static Discharge - is a transfer of energy between two opposite charged objects. An annoying slight jolt can be felt when working inside the chassis of the computer. Due to this static shock, computer components especially CMOS components which are incredibly sensitive to static shock can suffer irreperable damage and the battery will malfunction. Take extra precautions; always remember to ground yourself to eliminate static shock -- touch the unpainted metal part of computer case.

• Defective Battery - Battery dies off prematurely before its expected time.

• Non-use of computer (power cord is unplugged) for a very long period of time - say for several months.
  

1. Turn on your computer again.

2. If you still get the same error message again, unplug the power cord since you can't turn it off properly.

3. Wait for a couple of minutes.

4. Press the power button few times.

5. Reconnect the power cord and press the power button to turn on the PC.

6. If the error message appears again, then you need to buy a new CMOS battery.

7. If it boots up fine and the time and date is correct, the battery is fine.

Warning: Ground yourself by touching the exposed unpainted metal in the computer to avoid static shock and transferring the static electricity to the CMOS components that may cause damage.

1. Disconnect the power cord and unplug all the cables at the back of the tower computer.

2. Turn it on its side with the case access panel facing towards you.

3. Unscrew to remove the panel.

4. Locate the battery on the motherboard. It looks like a silver coin.

5. Push the spring clip at the side with a flat screw driver so that the battery will dislodge from its seat. (See the video at the right.)

6. Replace with a new one.

7. Reconnect all the cables and plug the power cord.

8. Click F2 and reset date and time.

9. Save your setting.

Make sure that you buy the same exact type of CMOS battery. You can either bring and show the old one to a sales representative or write down the information written on it.

Removing and replacing CMOS battery is quite so simple by carefully following my instructions above. You can do it yourself without having to ask someone to do it for you.