Your Dell computer's motherboard battery, sometimes called the backup battery, is a small, coin cell battery that powers the CMOS (Complementary Metal Oxide Semiconductor) chip built into the motherboard. This chip stores data essential to your computer's basic operation. Since this battery is connected directly to the motherboard, you will have to partially dismantle your Dell desktop to access the CMOS. Fortunately, for most Dell computers this is not a difficult procedure.
Power down the computer by using the operating system's start menu. Disconnect all cables and devices from their sockets on the computer's back panel.
Rotate the computer so the back panel is facing toward you. Lay the computer tower on its left side. Lift the retaining latch on the back panel. This latch secures the right side access panel in place.
Grasp the moulded grip on the computer's side access panel. Remove the panel from the computer to reveal the inside of the computer.
Locate the CMOS battery socket in the centre of the motherboard near the processor chip. Use a small flat head screwdriver to carefully pry the battery out of its socket.
Place the new CMOS battery into the empty socket. Press on the top of the battery until it snaps into place.
Replace the side access panel. Place the computer tower vertically. Then reconnect all cables and devices to the computer.