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Components Article Last Reviewed September 2009 |
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 How To Install A CMOS Battery |
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The problem would be funny if it weren't so annoying: A tiny battery that costs just a couple of dollars can single-handedly bring your high-tech PC screeching to a halt. The CMOS (complementary metal-oxide semiconductor) battery is located on your computer's motherboard. The CMOS is just a little battery, not much unlike what you could find powering a handheld calculator. When that battery starts to run out of power, unpleasant things will happen. For example, you may notice the PC keeps forgetting the date and time, resetting them to midnight on Jan. 1, 1990, perhaps. Or the PC suddenly can't access certain peripherals. Or it may refuse to boot at all, displaying a "CMOS Checksum Error" or "System Configuration Lost" message instead. Let's first back up and provide some background. Your computer's BIOS (Basic Input/Output System) is the traffic controller for all of the PC's hardware. The BIOS is responsible for booting the computer, keeping track of the time, and reading the keys that you type on the keyboard. It also makes sure the CPU can talk to the motherboard, the hard drives can talk to the IDE (Integrated Drive Electronics) bus, and much more. The settings for the BIOS are stored in special memory called CMOS. A battery backs up the CMOS, so the computer's essential settings are retained when the computer is turned off. When that battery runs out of juice, however, the CMOS forgets the proper settings, and things stop working properly. A typical CMOS battery should last for years, perhaps even a decade, but numerous factors can reduce that time. If your computer is showing the symptoms of a bad battery, go ahead and consider replacing it.  Replace The Battery 1. Save your current BIOS settings. When you remove the old battery from the motherboard, the information that's stored in the CMOS will be lost, so you should write down the BIOS settings. If the battery is already completely drained, your CMOS settings have already been lost, so you'll only need to take this step if you think the CMOS battery still has some life left in it. Turn the PC on. As soon as it powers up and beeps, press the appropriate key to enter the BIOS setup utility. This method varies among computers, but you can often access the setting by pressing the DELETE, ESC, or F2 key. The information screen that appears when you first turn on the PC will tell which key to press on your system. The simplest route, though, may be to simply check your system's manual. You'll see the main menu of the BIOS setup utility. You'll probably have to use the keyboard to navigate the BIOS, although a few setup utilities include mouse support. Navigate to every setup screen and write down the configuration settings. If you have a printer that uses a parallel port rather than a USB (Universal Serial Bus) port, you may be able to save some time by pressing the PRINT SCREEN key to print each configuration screen. Alternatively, some motherboards include software—either as part of the BIOS setup utility or as separate software—that saves CMOS settings to a floppy diskette. Check your system manual to find out if yours does. 2. Get access to the motherboard. Unplug your computer and disconnect the various cables. Remove the case's side panel to reveal the motherboard. Move the computer to an area that isn't crackling with static electricity, such as rooms with carpet. Static electricity can wreak havoc with your motherboard and computer components, so don't continue working while wearing stockings on a plush carpet as the cat rubs herself on the computer. It's a good idea to use an antistatic wrist strap whenever you're working inside a computer.
3. Locate the battery. You'll need to know what type of battery you need. Check your PC's manual or just examine the motherboard itself. The most common type of CMOS battery is CR2032, a round, silver-colored battery about the size of a dime. If your motherboard uses a CR2032, you're in luck. They're inexpensive, easy to replace, and widely available. You can buy one for about $4 at the photo counter of your local drug store, RadioShack, or an online vendor. 4. Remove the old battery. Next, remove the old battery. Different motherboards have various configurations of clasps that keep the battery clipped to the motherboard. Figure out how the battery is attached and gently remove it. Be careful not to break the retaining clips or anything else on the motherboard.
In the several motherboards we've used, it was possible to remove and replace the battery without taking out any peripherals. But it's possible that on your system an optical drive, add-on card, or other internal component will block easy access to the battery. If you're not comfortable removing and reinstalling those components, bribe a friendly neighborhood computer geek to help.
Turn the PC on and press the appropriate the key to start the BIOS setup utility. Methodically go to every setup screen and set the values to the settings you wrote down or printed. Or, if you backed up the BIOS settings with the motherboard's backup software to floppy diskette, use it to restore the settings. Either way, don't forget to reset the date and time.
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