HP -18C Owner's Manual page 188

To install batteries:
1. Have three fresh N-cell batteries readily at
hand.
2. Open the calculator to expose the keyboard and display. If you
are replacing batteries, make sure the calculator is off.
Do not
press
I
ON
I
until the entire procedure for changing batteries is
completed. Changing batteries with the calculator on could
erase the contents of Continuous Memory.
(If you have any
pending alarms stored in memory, check to make sure no alarm
will come due while the batteries are out.)
3. Hold the calculator with the battery compartment door facing
up. To remove the battery compartment door, slide it towards
the back of the calculator (away from the product label).
Figure C-1. Removing the Battery Compartment Door
4. Tip the calculator to remove the old batteries.
5. Insert three new batteries. Orient the batteries as shown on the
diagram on the back of the calculator. Be certain to observe the
polarities (+ and -) as shown.
6. Press the batteries into the compartment using the portion of the
battery door that extends beyond the metal contact plate. Press
down until the contact plate is lined up with the grooves on the
calculator case.
186 C: Caring for and Using Your Calculator