All personal computers have a small battery on the motherboard that provides power to the Complementary Metal Oxide Semiconductor (CMOS) chip, hence the name CMOS battery. The chip has the information about all the system's configuration, such as the hard disk, date and time, etc. It provides power even when the computer is off and allows the CMOS to save all the settings [source: Indiana University]. You can expect the CMOS battery to last for up to five years. The more your computer is used, the longer the battery will last. How do you know that your CMOS battery is dying? Here are some tell-tale signs that your battery is dying:

  • Invalid configuration will appear on your screen.
  • Run Setup appears on your screen.
  • Press F1 to continue appears on your screen.
  • Invalid drive specification appears on the screen after you've pressed F1.
  • Clock Error or Clock Message appears on your screen.
  • The clock on the computer loses time.
  • The computer is constantly showing the wrong date.

Should you experience any of these symptoms, it's time to change the battery in your computer. If you don't change the battery, the battery will die. Your battery is dead when your screen is blank and you have thus lost your CMOS memory [source: Smart Computing].