Computer Clock Losing Time Due to CMOS Battery Depletion

This is the most common cause of time loss. Confirm this by checking the voltage of the CR2032 coin-cell battery located on the motherboard using a multimeter. A healthy battery must measure greater than 3V. If the voltage is significantly lower than 3V, or if the system resets to a factory default date every time the computer is disconnected from main power, the battery is confirmed to be depleted.