FJCruiser battery discharge issue

Had a similar issue with my 2019 Audi A4. Sounds like your battery sensor might be defective. Also check the battery terminals for corrosion and ensure they're properly tightened. A faulty sensor can cause battery drain even when the car is off. Have you checked the battery voltage when the car is running and off?

Thanks for the response. I haven't checked the voltage yet. Could you explain how to properly check it and what readings would indicate a defective sensor?

Using a multimeter, check the voltage across the battery terminals with the engine off; a healthy battery should read around 12.6 volts. Then, start the engine and check again; it should be around 13.7 to 14.7 volts, indicating the alternator is charging. If the voltage is significantly lower in either test, or fluctuates erratically, the sensor or charging system may be at fault. Based on my experience and your symptoms, I'd recommend a workshop; they can properly diagnose it.

Appreciate the detailed explanation and advice. Took it to a trusted workshop for diagnosis. They confirmed the battery sensor was defective, and the repair cost 315€. Thanks again for your help!