Other Information
Replacement of the battery (main battery)/ battery monitoring sensor
For replacing the battery (main battery) or battery monitoring sensor, battery information must be reset. See: VIDA/DIAGNOSTICS/VEHICLE COMMUNICATION/CEM/Advanced.
The vehicle's battery (main battery) is completely discharged or the battery monitoring sensor has been disconnected from the battery pole.
If the battery (main battery) has been completely discharged so that the vehicle does not react to the ignition key (in principle, is completely dead) and the vehicle is then started using an external auxiliary battery or battery charger, the battery monitoring sensor can interpret this as it being disconnected from the battery (main battery). The battery monitoring sensor then reads off the battery voltage and assumes a SoC that is proportional to the voltage. If the SoC is low, the automatic start/stop of the engine function is not permitted.
For the battery monitoring sensor to calculate the main battery's correct state of charge the vehicle must be in sleep mode for 4 hours. Sometimes, 6 hours in sleep mode may be required. This is on the condition that the ignition key has been removed, doors and hatches closed and the car is locked. If the SoC is still low, the automatic start/stop of the engine function will not be permitted. The battery (main battery) then needs to be charged.
Charging battery (main battery)
When the external auxiliary battery or battery charger is temporarily connected, the battery's (main battery) negative pole must never be used for connection, only the vehicle's chassis must be used as an grounding point. When connected correctly, the battery monitoring sensor registers how much current the battery (main battery) is charged with and can then calculate the battery's (main battery) correct SoC.
Secondary battery relay always activated/closed
If the vehicle's battery (main battery) is disconnected with the ignition off and the secondary battery relay is continuously activated/closed for some reason, the vehicle will still be powered.
To check this, connect the battery's (main battery's) negative pole. Then try switching on the ignition. If the vehicle's ignition can be switched on, there is probably a fault in the secondary battery circuit.