HP -80 Owner's Handbook Manual page 72

Temporary degradation, peculiar to nickel-cadmium batteries, may
cause a decrease in the operating period of the battery pack. Should
this happen turn the HP-80 on for at least five hours to discharge the
batteries completely. Then put it on charge for at least 14 hours. This
should correct the temporary degradation.
If the battery pack won't hold a charge, it may be defective. If the
warranty is in effect, return the pack to Hewlett-Packard according to
the instructions on page 74. If the battery pack is out of warranty,
use the Accessory Order Card provided with your HP-80, to order a
new battery pack. Remember, you can use your
UP-SO
on ac power
until the replacement battery pack arrives.
Battery Pack Replacement
1. Turn power switch to OFF and disconnect the battery charger.
2. Slide the two battery-door latches (the top feet) toward middle of
calculator.
3. Let battery door and battery-
pack fall into palm of hand.
70
4. - See if the battery connector
springs on the calculator ha ve
been inadvertently flattened
inward. If so, bend them out
and try the battery again.