•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.