Radio Shack TRS-80 PC-3 Owner's Manual page 80

To recharge the battery, turn the Computer and Printer/Cassette Interface power OF F, connect the AC adapter to the Printer/
Cassette Interface, and plug the AC adapter into a wall outlet. (See the diagram.) It will take about 15 hours before the battery
is fully charged.
Important Note! Using any AC adapter other than the one supplied may damage the Printer/Cassette Interface.
PC-3 PR INTER/CASSETTE-----+
INTERFACE
AC ADAPTER
AC ADAPTER CONNECTING
JACK OF PC-3 PRINTER/
CASSETTE INTERFACE WALL OUTLET
Figure 16. How to Connect the AC Adapter
Always connect the recharger to the Printer/Cassette Interface first. Then plug the recharger into the wall socket.
When the batteries in the PC-3 Printer/Cassette Interface become discharged, the low battery indicator on the front of the unit
lights up and the unit will not function. At this point, you must recharge the batteries. When you first receive your Printer/
Cassette Interface it is likely that the batteries insufficiently charged due to the time spent in storage. The unit will require charging
before its first use.
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