•Switch off all electrical consumers and the ignition.
•Unlock the vehicle before disconnecting the battery in order to avoid triggering the anti-theft
alarm.
•First disconnect the negative cable and then the positive cable ⇒.
Connecting the 12-volt vehicle battery
•Switch off all electrical consumers and the ignition before reconnecting the 12-volt vehicle
battery.
•First reconnect the positive cable and then the negative cable ⇒.
Various indicator lamps may light up after the 12-volt vehicle battery has been connected and the
ignition is switched on. They will go out if you drive a short distance at a speed of approximately
15 – 20 km/h (10 – 12 mphyf , I W K H L Q G L F D W R U O D P S V U H P D L Q O L W X S W K H Y H K L F O H V K R X O G E H F K H F N H G E \ D
qualified workshop.
If the 12-volt vehicle battery was disconnected for an extended period, the system may not able to
calculate or correctly display the time when the next service is due ⇒ Instrument cluster. Observe
the maximum permissible service intervals ⇒ Service.
Vehicles with Keyless Access:⇒ Central locking system: if the ignition cannot be switched on after
connecting the 12-volt vehicle battery, lock and unlock the vehicle from the outside. Then try to start
the ignition again. Please contact an expert if the ignition cannot be switched on.
Automatic switch-off for electrical consumers
The intelligent vehicle electrical system management automatically implements a range of
measures to prevent the 12-volt battery from discharging under high loads:
•The idling speed is increased so that the alternator provides more electricity.
•The performance of large electrical consumers may be reduced or they may be switched off
completely.
•The power supply to the 12-volt socket and the cigarette lighter is interrupted temporarily while
the engine is being started.
The vehicle electrical system management function cannot always prevent the 12-volt vehicle
battery from discharging. For example when the ignition is switched on for an extended period with
the engine off, or when the side or parking lights are on when the vehicle is parked for an extended
period.
Battery switch-off in an accident in which the airbag is triggered
In vehicles with 12-volt vehicle battery in the luggage compartment, the electrical connection to the
12-volt vehicle battery is disconnected pyrotechnically in the event of an accident in which the
airbags are triggered. This prevents short-circuiting.
What can cause the 12-volt vehicle battery to discharge?
•Long periods at a standstill in which the engine is not running, especially if the ignition is
switched on.
•The use of electrical consumers when the engine is switched off.
•When the auxiliary heater is being used ⇒ Auxiliary heater and ventilation.
