The CMOS battery is a small unit located on the motherboard of most computers, which provides the electricity needed to keep the current time and system configuration settings while the computer is turned off. When the battery fails, the computer will have to spend time detecting what type of disk drives it has every time it boots up, the time and date will be incorrect, and there may be other problems depending upon its specific configuration. This can happen with normal use, although it is more likely on computers which haven’t been used for many months. Replacement of the battery should fix these problems after the settings have been corrected.
If you pay someone else to service your computer, it might be a good idea to ask them to replace the CMOS battery preventively, if it hasn’t been replaced for several years. This would probably be less costly than having the computer serviced again just for replacement of the battery.
To replace the battery yourself, you will first need to determine what type it is. You may be able to find out what type of CMOS battery your computer uses in its owner’s manual or on the internet, unless it is a generic model. You might also determine this by looking inside the computer, although it is not always obvious which part is the battery. The majority of desktop and tower-style computers made in the mid-1990s and later have round, shiny CR2032 batteries, which are relatively inexpensive. Computers manufactured before the mid-90s and laptops can have any one of a wide variety of CMOS batteries, including the CR2032. Some computers from the 1980s and very early ’90s don’t have CMOS batteries at all; some store configuration data on an EEPROM, others detect their configurations at each start-up. There may be less expensive replacement batteries equivalent to the battery listed in the computer’s manual; for example, a Radio Shack 23-162 is the same as a CR2032.
Replacement CR2032 batteries can be purchased at Radio Shack, Sam’s Club, and many websites. eBay.com is one of the least expensive places to buy them, especially if they are generic. Sets of five or more usually cost substantially less per-unit; buying them this way might be a good idea if you have two or more computers. Other types of CMOS replacement batteries are harder to find and generally more expensive. Office Depot stores carry a few types of these. Searching for “[laptop brand name] [laptop model] cmos battery” on eBay.com can often bring up listings for laptop-specific CMOS batteries, and Google Product Search (google.com/products) frequently provides additional results.
After the correct replacement CMOS battery has been purchased, the old battery will have to be removed from the motherboard. This is usually not difficult, although it varies from one computer to the next. Before removing it, you should record the computer’s BIOS settings if they haven’t already been lost. Some laptops and pre-486 desktop computers have soldered-in CMOS batteries; these cannot be removed, but there might be a location for connecting a new battery. Refer to the manual if possible, and look to see if there are any diagrams printed on the inside of the computer’s casing. After removal, do not discard it immediately; first insert the replacement battery to make sure it fits, then start up the computer to verify that the problem was indeed caused by the battery failing.
Following these tips should help you complete the replacement of your computer’s CMOS battery with the least difficulty and expense.