The desktop computer you're fixing won't save the correct time and date. You set the time and date, then turn off and on the system. The settings are once again incorrect. Which component is MOST LIKELY to be at fault?

When the BIOS/UEFI fails to retain your computer's settings, such as time and date and hard disk configuration, this is a regular problem. To assist it retain settings when the system power is turned off, the BIOS/UEFI uses a small battery (similar to a watch battery) on the motherboard. If this battery fails, the BIOS/UEFI settings will be lost. To resolve the issue, simply change the battery.