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 equipment is in use when the engine is not running. 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 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. Certain convenience features, such as remote control unlocking, may not be available. These functions will be restored when you switch on the ignition and start the engine.
With the engine switched off
If you listen to the radio or use other electrical equipment when the engine is not running, this will discharge the battery.
On vehicles with driver information system*, a message will appear before the battery power drops to a level where the starting ability is impaired.
This message advises you to start the engine in order to recharge the battery.
When the engine is running
Although the alternator generates electrical power, the battery can still become discharged while the vehicle is being driven. This can occur when a lot of power is being consumed but only a small amount supplied, especially 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 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 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.