How to Replace a CMOS Battery

All desktop and laptop computers use a special battery called a Complementary Metal Oxide Semiconductor (CMOS) battery which stores information about your computer, such as the date and time, when the machine is powered off. Normally the battery re-charges itself whenever the computer is turned on but if it stops working or becomes damaged you will need to replace it manually.

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Replace a CMOS Battery

Step

Unplug the power cord from the power supply on the back of your computer. Remove all of the extra cables for the mouse, keyboard, monitor, printer and speakers.

Step

Use a screwdriver to unscrew the case screws on the side of your computer. Put pressure on the side panel and slide it off the case.

Step

Locate the small circular battery, which will usually be either color or silver-colored, near the center of the motherboard. Check the model number on the top of the battery and then purchase a replacement through an online electronics store or a local computer supply store. Make a note of the model information on the battery as you may need it to complete the installation.

Step

Snap off the battery cover if your motherboard has one and then remove the CMOS battery by simply pulling it out of its holder.

Step

Push the replacement battery back into the battery slot and pop the cover back down. Put the side panel back on the case, re-attach all of the cables, and then power on your computer to ensure the battery was correctly installed. Wait to see if the computer changes to a prompt asking for the battery information or if it boots directly to the desktop.

Step

Enter in the battery model information you wrote down earlier if the prompt asks for it and then hit "enter" to finish the installation.