HP xw4000 Hardware Reference Manual page 56

RTC Battery Replacement
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C–4
c. To insert the new battery, slide one edge of the replacement
battery under the holder's lip with the positive (+) side up.
Push the other edge down until the clamp snaps over the other
edge of the battery.
CAUTION: For proper operation, position the battery with the
positive (+) side up. Follow the battery handling precautions/warnings
documented at the beginning of this section.
Replacing a Coin Cell Battery (Type 2)
After the battery has been replaced, use the following steps to
complete this procedure.
5. Replace the computer cover or access panel.
6. Plug in the computer and turn on power to the computer.
7. Reset the date and time, your passwords, and any special system
setups, using Computer Setup. Refer to the Computer Setup
Guide.
If you normally lock the Smart Cover Lock, use Computer Setup to
relock the lock and enable the Smart Cover Sensor.
Hardware Reference Guide