Cessna SkyHawk SP 172S NAV III 2005 Pilot Operating Handbook page 106

CESSNA
MODEL 172S NAV III
SECTION 3
EMERGENCY PROCEDURES
SUPPLY
ELECTRICAL POWER
MALFUNCTIONS
(Continued)
INSUffiCIENT RATE-Of-CHARGE (Continued)
SYSTEMI
Main battery life can be extended by setting the MASTER switch
(ALT and BAT) to OFF and operating the equipment on the ESS
BUS from the standby battery. The standby battery is only capable
of providing power for systems on the Essential Bus and cannot
provide power for transponder (XPDR) operation. Main battery life
should be extended, when practical, for possible later operation of
the wing flaps and use of the landing light (at night).
NOTE
The LOW VOLTS annunciator can come on when
the engine is operated at low RPM with a high
electrical load. The LOW VOLTS annunciator will
usually go off when the engine is operated at higher
RPM for greater alternator system output. Make
sure that the M BAn AMPS indication shows
positive (+) current at the higher RPM.
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172SPHAUS-01
U.S. 3·35