HP HP-21 - Page 56

54 Accessories, Service, and Maintenance
Your calculator contains a rechargeable battery pack. The
batteries must be in the calculator for it to operate. With the
batteries in the calculator and the charger connected between
the calculator and the line, the battery will charge with the
calculator OFF or ON. Normal charging times from dead
battery to full charge are: Calculator ON 17 hours
Calculator OFF 6 hours
Shorter charge periods will reduce battery operating time.
Whether the calculator is OFF or ON, the HP-21 battery pack
is never in danger of becoming overcharged with the charger
connected to the ac line. It is normal for both the calculator and
the charger to be warm to the touch during charging.
CAUTION
Attempting to operate the HP-21 from the ac line with
the battery pack removed may result in damage to
your calculator.
The procedure for using the battery charger is as follows:
1. If your charger has a line voltage select switch, make sure
it is set to the proper voltage. The two line voltage ranges
are 100 to 127 volts and 200 to 254 volts.
CAUTION
Your HP-21 may be damaged if it is connected to the
charger when the charger is not set for the correct
line voltage.
2. Set the HP-21 power switch to OFF.
3. Insert the battery charger plug into the rear connector of
the HP-21 and insert the power plug into a live ac power
outlet.
4. Atthe end of the charging period, you may continue to use
your HP-21 with ac power or proceed to the next step for
battery-only operation.
5. With the HP-21 power switch turned OFF, disconnect
the battery charger from both the power receptacle and
the HP-21.
CAUTION
The use of a charger other than the HP battery charger
supplied with the calculator may result in damage to
your calculator.