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188 Intelligent technology
Depending on the power level of the battery, the individual electrical com-
ponents are switched off one after the other to prevent the battery from los-
ing too much charge and to ensure that the engine can be started reliably.
Dynamic power management
While the vehicle is moving, this function distributes the available power to
the various electrical components and systems according to their require-
ments. The power management ensures that on-board systems do not con-
sume more electrical power than the alternator can supply, and thus main-
tains the maximum possible battery power level.
Note
● The power management system is not able to overcome the given physi-
cal limits. Please remember that the power and useful life of the battery are
limited.
● When there is a risk that the vehicle will not start, the alternator power
failure or low battery charge level warning lamp will be shown
⇒ page 69.
Note carefully
Starting ability has first priority.
Short trips, city 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 supplied. The situation is also critical if electrical equip-
ment is in use when the engine is not running. In this case power is con-
sumed 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 periods
If you do not drive your vehicle for a period of several days or weeks, the
power management will gradually shut off the on-board systems one by
one, or reduce the amount of current they are using. This limits the amount
of power consumed and helps to ensure reliable starting even after a long
period. Some convenience functions, such as remote vehicle opening, may
not be available under certain circumstances. These functions will be re-
stored 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 appear in vehicles with a driver information system*.
This driver indicator tells you that you must start the engine so that the bat-
tery can recharge.
When the engine is running
Although the alternator generates electrical power, the battery can still be-
come discharged while the vehicle is being driven. This can occur when a
lot of power is being consumed but only a small amount supplied, especial-
ly if the battery is not fully charged initially.
To restore the necessary energy balance, the system will then temporarily
shut off the electrical components that are using a lot of power, or reduce
the current they are consuming. Heating systems in particular use a large
amount of electrical power. If you notice, for instance, that the seat heating*
or the heated rear window 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 electrical power is available.
You may also notice that the engine runs at a slightly faster idling speed.
This is quite normal, and no cause for concern. The increased idling speed
allows the alternator to meet the greater power requirement and charge the
battery at the same time.
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