CHEVROLET Tahoe - Manual (Page 221)

The battery can be discharged at idle if the
electrical loads are very high. This is true for
all vehicles. This is because the generator
(alternator) may not be spinning fast enough at
idle to produce all the power that is needed for very
high electrical loads.
A high electrical load occurs when several of the
following loads are on: headlamps, high beams,
fog lamps, rear window defogger, climate
control fan at high speed, heated seats, engine
cooling fans, trailer loads, and loads plugged into
accessory power outlets.
EPM works to prevent excessive discharge of the
battery. It does this by balancing the generator’s
output and the vehicle’s electrical needs. It
can increase engine idle speed to generate more
power, whenever needed. It can temporarily
reduce the power demands of some accessories.
Normally, these actions occur in steps or levels,
without being noticeable. In rare cases at the
highest levels of corrective action, this action may
be noticeable to the driver. If so, a Driver
Information Center (DIC) message might be
displayed, such as Battery Saver Active or Service
Battery Charging System. If this message is
displayed, it is recommended that the driver
reduce the electrical loads as much as possible.
See DIC Warnings and Messages on page 270.
Battery Run-Down Protection
This feature shuts off the dome, and reading
lamps if they are left on for more than 10 minutes
when the ignition is off. This will keep the
battery from running down.
221