Honeywell T8665C EnergyPro Owner's Manual page 71

MPORTANT
4. If you insert new batteries within 20 to 30
seconds of removing old batteries, the
system retains current time and day. If the
display is blank, batteries are dead or
installed incorrectly. You must reset time
and day. See Setting the Clock section.
As a precaution,
9
Although thermostat has a low battery
indicator, replace batteries yearly to
prevent leakage and thermostat and
heating/cooling system from shutting
down due to lack of thermostat battery
power.
when leaving home for longer
than a month, change
batteries before leaving to
prevent system shutting
down due to lack of power.
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