Compaq 247320-003 - Deskpro 4000 - 5166 Model 2500/CDS Reference Manual page 228

To prepare the computer, complete the following steps:
1. If you have locked the Smart Cover Lock, use Computer
Setup to unlock the lock.
For more information about Computer Setup, refer to
Chapter 8, "Using Compaq Utilities."
2. If the computer is on, turn it off.
3. Unplug the computer.
4. Remove the computer cover or side panel.
For more information about removing the computer
cover, side panel, and expansion board cage, refer to
Chapter 6, "Upgrading the Desktop Computer," or
Chapter 7, "Upgrading the Minitower Computer."
5. Remove the expansion board cage.
6. Refer to the following section for specific battery
installation steps.
The battery that came with this computer is non-removable and
is permanently installed on the system board. A second battery
is installed when the first becomes inoperative.
!
To install the replacement battery, complete the following steps:
1. Remove and discard the protective covering from the
adhesive backing on the hook-and-loop connector on the
back of the battery.
2. Attach the battery to the computer chassis as shown in the
following illustrations: