How to Replace a Compaq Presario CMOS Battery

By Leonardo R. Grabkowski

The CMOS battery in your Compaq Presario computer helps your PC keep the correct date and time. If the battery fails, you may experience problems with your computer because many features rely on the system keeping time. When the battery is low, you should see an error message when you start your computer. CMOS stands for Complementary Metal-Oxide Semiconductor. This battery is similar to a watch battery. It's located on your motherboard inside your Presario's tower.

Things You'll Need

  • Phillips screwdriver
  • ESD wrist strap
  • Replacement CMOS battery

Step 1

Shut down your computer through the Start menu and wait for the system to power off. Access the rear of the computer tower and unplug all of the cables and connections. Note their location before doing so. You should have three to five connections at the rear, including the monitor, mouse and keyboard.

Step 2

Pull the Presario tower out of its spot and lay it on its side. Remove the Phillips screws from the rear edge of the tower. There should be four to six screws depending on which Presario model you have. Lift the edge of the panel and remove it from the Presario tower to access the internal components.

Step 3

Wear your ESD strap. Attach the ground strap to an unpainted metal piece on your computer tower. This prevents electrostatic discharge, which can wreak havoc on your computer.

Step 4

Locate the battery on the main circuit board. It should be easily visible inside. The CMOS battery is a small, silver, circular battery, very similar to a watch battery. Note the position of the battery (the direction of the positive and negative sides). This helps when installing the new one.

Step 5

Slide the battery out of its slot or mount. On some Presario models, the battery is positioned vertically--this requires lifting straight up. On others, the battery lays flat. You may have to gently pry the edge of the battery to remove it.

Step 6

Match up the new CMOS battery with the old CMOS battery. Make sure that the batteries have the same number on them. A common battery is CR2032--however, this may vary between Presario models.

Step 7

Install the new CMOS battery into the slot exactly as the previous one was. Slide the tower panel back over the Presario tower and tighten the screws. Reconnect the cables and attachments to the rear of your Presario tower. Power your PC back on.