The CMOS (complementary metal oxide semiconductor) battery in the computer is used to store the hardware configuration settings. It also keeps a record of the date and time when the computer is switched off. The CMOS battery is inside the computer and attached to the system board (motherboard).
CMOS battery life varies based on the usage and environment of the computer (usually around 2-3 years). The most common symptom of CMOS battery failure is incorrect or slow system date and time in the BIOS, loss of BIOS settings when the computer is powered off, time-of-day clock stopped error message and so on. If the CMOS battery is out of charge, the BIOS settings will be lost when the computer is powered off. You will prompted to reset the time and date when you power on the computer. Sometimes the loss of BIOS settings may prevent the computer from loading the operating system.
Before you begin, read and follow the safety instructions in Dell Knowledge Base Article - Precautionary Measures for Personal Safety
- Disconnect the power cable of the computer.
- Discharge static electricity by pressing and holding the power button for 10-15 seconds.
- Replace the battery with the exact same type of coin cell battery. Dell desktops use CR2032 coin cell battery (see the markings on the battery). See the User Guide for model-specific information.
- Removing the CMOS battery erases the BIOS settings
- Ensure to replace with a brand new battery. Do not install a used battery.
- Properly dispose the used batteries as directed by the local authorities.
- Use an anti-static plastic scribe tool. Do not use any kind of metal object to pry the battery.
- To avoid damage to the battery connector, firmly support the connector while removing the battery.
Dell desktop computers use a 3V lithium battery (CR2032) that is also used on wrist watches and other small electronic devices. See the User Guide for model-specific information. The flat side of the battery is always positive (+).
WARNING: Disconnect all power sources before opening the computer cover or panels. After you finish working inside the computer, replace all covers, panels, and screws before connecting to the power source.
CAUTION: To avoid electrostatic discharge, ground yourself by using a wrist grounding strap or by periodically touching an unpainted metal surface at the same time as touching a connector on the back of the computer.
- Browse to Dell Manuals website.
- Identify your Dell desktop:
- Enter the model number or Service Tag of the Dell desktop, and then click Search.
- Or, click Browse all products, select Desktops & All-in-Ones, and select your Dell desktop from the catalog.
- Under the Documentation tab, scroll to the Manuals and Documents section and click View PDF next to the monitors User Guide or Service Manual.
- Scroll to the Coin cell battery section.
- To remove the CMOS battery, follow the instructions under the Removing coin cell battery section.
- To install the CMOS battery, follow the instructions under the Installing the coin cell battery section.
To learn about BIOS, see the Dell knowledge base article Dell BIOS Updates.