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Practical tips
consume more electrical power than the al-
t
ernator can supply, and thus maintains the
maximum possible battery power level.
Note
●
Neither is the po
wer management system
able to overcome the given physical limits.
Please remember that the power and use-
ful life of the battery are limited.
●
If there is a risk that the vehicle may not
start, the alternator electrical failure or low
battery charge level warning lamp will be
shown
›››
page 318.
Flat battery
Starting ability has first priority.
Short trips, cit
y traffic and low temperatures
all place a heavy load on the battery. In
these conditions a large amount of power is
consumed, but only a small amount is sup-
plied. The situation is also critical if electrical
devices are in use when the engine is not run-
ning. In this case power is consumed when
none is being generated.
In these situations you will be aware that the
power management system is intervening to
control the distribution of electrical power.
When the vehicle is parked for long peri-
ods
If you do not drive your vehicle for a period of
several days or weeks, the power manage-
ment will gradually shut off the electrical de-
vices one by one or reduce the amount of
current they are using. This limits the amount
of power consumed and helps to ensure reli-
able starting even after a long period. Some
convenience functions, such as remote vehi-
cle opening, may not be available under cer-
tain circumstances. These functions will be
restored when you switch on the ignition and
start the engine.
With the engine switched off
For example, if you listen to the sound system
with the engine switched off the battery will
run down.
If the energy consumption means there is a
risk that the engine will not start, a text will be
displayed in vehicles with a driver information
system.
This driver indicator tells you that you must
start the engine so that the battery can re-
charge.
When the engine is running
Although the alternator generates electrical
power, the battery can still become dis-
charged while the vehicle is being driven. This
can occur when a lot of power is being con-
sumed but only a small amount supplied, es-
pecially if the battery is not fully charged ini-
tially.
To restore the necessary energy balance, the
system will then temporarily shut off the elec-
trical devices that are using a lot of power, or
reduce the current they are consuming. Heat-
ing systems in particular use a large amount
of electrical power. If you notice, for instance,
that the seat heating or the rear window
heater is not working, they may have been
temporarily switched off or regulated to a
lower heat output. These systems will be
available again as soon as sufficient electri-
cal power is available.
You may also notice that the engine runs at a
slightly faster idling speed when necessary.
This is quite normal, and no cause for con-
cern. The increased idling speed allows the
alternator to meet the greater power require-
ment and charge the battery at the same
time.
320
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