Mini One Diesel Battery Error

Sounds like a similar issue I faced with my Mini One. I also experienced a battery malfunction and electrical problems. Have you checked the voltage drop across the battery terminals while attempting an engine start? A significant voltage drop could indicate a failing battery. Also, the power management system in these cars is quite sensitive, so even a slightly weak battery can trigger those error messages. It's probably the battery, to be honest.

Thanks so much for your quick response! When you say 'voltage drop', what exactly do you mean, and how would I check that? I'm not very technical, I have to admit. Is that something I could do myself, or should I just take it to a professional?

By voltage drop, I mean the decrease in voltage when you try to start the engine. A healthy battery should maintain a relatively stable voltage during engine start. If it drops significantly (below 10V), it suggests the battery is weak and unable to supply enough current. While you could check it yourself with a multimeter (a device used to measure voltage), considering you're not very technical, it's probably best to take it to a workshop. They can properly diagnose the issue and confirm if a battery replacement is needed. It does sound like the battery to me, though, given all the symptoms you describe.

Just wanted to give a quick update! I took your advice and brought my Mini to the workshop. Turns out, the auxiliary battery was indeed faulty and not holding a charge. After the battery replacement, all the error messages disappeared and the engine starts like a charm again. The final bill was 290€, which is what I expected. Thanks again for your help!