Mini Cooper Diesel Weak Battery and Flickering Lights

Weak battery and flickering lights on a Mini Cooper Diesel definitely sounds like a potential battery or charging system issue. First, have you checked the battery terminals for any corrosion or loose connections? Even a small amount of corrosion can cause significant voltage drop. Also, do you have access to a multimeter? If so, you could check the battery voltage with the engine off (should be around 12.6V) and then with the engine running (should be around 13.7-14.7V). This will give you an idea of whether the alternator is charging the battery properly. Low voltage could certainly point to a faulty battery sensor, which can mess with the charging system. Have you noticed any other electrical issues, like the radio cutting out or the dashboard lights dimming unexpectedly?

Thanks for the quick response! I did check the battery terminals, they looked clean. I don't have a multimeter myself, but a friend does. When checking the voltage with the engine running, what should I look for exactly? If it's outside that 13.7-14.7V range, does that confirm the battery sensor is bad, or could it be something else?

Okay, given that you've already checked the terminals and suspect the battery sensor based on diagnostics, I'd say it's highly likely that's the culprit. While voltage readings outside of the 13.7-14.7V range could indicate other issues like a failing alternator, a faulty battery sensor can absolutely cause similar symptoms by providing incorrect information to the car's computer, leading to undercharging or overcharging. Given the age of your Mini and the mileage, a failing sensor is a common issue. I would advise against trying to fix it yourself unless you are very familiar with car electrics. Given the diagnostic result and your symptoms, I'd recommend taking it to a reputable mechanic or the dealer for a proper diagnosis and sensor replacement. It is unfortunate that the repair cost is 315€, but you may risk frying other components.

Okay, I finally got it sorted! Took the Mini to a trusted mechanic, they ran diagnostics and confirmed it was the battery sensor. They replaced it, and now the charging system seems to be working perfectly. No more flickering lights or struggling to start! Cost me around 315€, but at least it's fixed. Thanks a lot for your help, your insights really pointed me in the right direction!