Viano diesel battery drain and sensor problems

Sounds like a parasitic battery drain. First, confirm the battery's condition with a load test; even new batteries can fail. Check the resting voltage after sitting overnight; it should be above 12.6V. Then, monitor battery charging voltage while the engine is running; it should be around 14V. Have you checked for current draw when the car is off? Anything above 50mA is excessive. A defective battery sensor is possible, but rule out other causes first. What error codes are you seeing?

Thanks for the reply. I will check the battery resting voltage and charging voltage as suggested. How would I isolate the circuit causing the battery drain to confirm if it's the battery sensor?

Isolating a parasitic draw requires a multimeter and patience. Start by disconnecting the negative battery terminal and placing the multimeter in series between the terminal and the cable. With the car off and all accessories disabled, observe the current draw. Then, systematically pull fuses one by one, noting any significant drop in current. When the current drops substantially, you've identified the circuit with the drain. From there, you can consult wiring diagrams to pinpoint the components on that circuit, including the battery sensor and its associated wiring. Given the symptoms, however, a trip to a workshop with diagnostic capabilities might be more efficient. The SDS can pinpoint battery related issues.

Appreciate the detailed explanation. I performed some basic checks, but isolating the draw is proving time-consuming. I took it to a local shop, and they confirmed the battery sensor was indeed the issue. Repair cost was 315€. Thanks again for your help.