Dead CMOS Battery

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On an older PC, it is normal for the CMOS battery to fail at some point in time. They usually last for many years, with over five years being the norm, at least on older machines. On a new motherboard, this sort of problem is usually a sign of a defect, although, you shouldn't worry about it if it appears only the very first time the board is powered up or after you replace the battery. Often, a dying battery will first manifest itself intermittently. Sometimes, you will boot with no problem. At other times, you will see an error indicating that the system doesn't match the configuration or you will see that the Date and Time settings on your computer are wrong. When the battery fails entirely, these errors will either come up every time you reboot, or your BIOS may report an error number with a message stating that the battery is dead. The solution is replacing the battery -- for detailed instructions for replacing the battery see the Replacing Hardware page.

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If you notice that your real-time clock is consistently losing time, or if you receive an error while booting that indicates your CMOS (complementary metal-oxide semiconductor) battery failed, you might have a failing or dead battery. Contact your motherboard supplier (or the motherboard manufacturer) for information about receiving and installing a new battery, or simply find a replacement and install it yourself. Some batteries are soldered onto the motherboards, so you may want to let a tech shop replace those. Other batteries are just held in place by a clip; and those are the ones that you can replace on your own. You can buy replacements online or at a computer store, but you must order the right type of battery for your motherboard. The motherboard manufacturer should be able to provide information as to an appropriate battery for the board, but may require a phone call or email. Some dead batteries may include specifications directly on the battery as well (specifically the flat batteries).