Battery Charging
When the external auxiliary battery or battery charger is temporarily connected, the battery's 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 awakes from its sleep mode as the current through the sensor (in to the battery) exceeds 250 mA. The sensor the registers how much current the battery is charged with and can then calculate the battery's correct charge status and capacity. When the current through the sensor is less than 250 mA the sensor continues in sleep mode.
If the battery's negative pole is used when charging, the battery monitoring sensor does not register the current that the battery is charged with. When the ignition is switched on, the battery monitoring sensor registers that the voltage across the poles has changed since the last registration. The battery monitoring sensor can interpret this as the calculation of the battery's SoC currently does not correspond (not reliable) and sends the message about this to the Engine control module (ECM). On these occasions the sensor's calculation of the battery status is not reliable and the function is therefore not permitted.
For vehicles with the automatic start/stop of the engine function, the function is not permitted temporarily.
The status of the sensor's calculation can be read off in VIDA (Volvo scan tool).
For the battery monitoring sensor to calculate the 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 brake energy regeneration function will not be permitted. The battery needs to be charged.