Radio Shack 20-501 - Manual (Page 12)

The Basics 12
If rechargeable batteries are installed and
ALKALINE/RECHARGEABLE is set to
RECHARGEABLE, the adapter powers the scanner
and recharges the installed batteries at the same
time.
Note: If the scanner does not operate properly
when you use a DC adapter, unplug the adapter
from the cigarette-lighter socket and clean the
socket to remove ashes and debris.