BMW 6 Battery Drain Issue: Bad Sensor or Battery Failure?

Hi there! I had a similar issue with my 2015 BMW 5 series diesel (I also own a 3 series). I've got some experience working with cars, mainly basic maintenance stuff. My symptoms matched yours exactly, warning lights, weak starts, and those annoying dim lights. Turned out the battery sensor was acting up, just as you suspect. Took it to my regular workshop and they confirmed it. Had it replaced for about 315 Euro all in. Before spending any money though, what's your vehicle's mileage and have you noticed any other electrical issues? Also, when was the last time you had the battery itself checked? This info would help determine if you're facing the same problem I had. Quick heads up, get it checked soon if you haven't already. Ignoring it could lead to getting stranded somewhere with a dead battery.

Thanks for sharing that experience! My BMW's at 143560 KM and had its last service about 2 months ago. The battery itself is actually fairly new, replaced it last winter. It's driving me crazy because everything was fine until these symptoms started showing up last week. The warning usually comes on after I've been driving for about 20 minutes, which made me think it might be more than just a battery issue. I'm planning to take it to a workshop this week, but wanted to check if anyone had similar experiences first. Really appreciate the heads-up about potential breakdown risks, definitely don't want to end up stranded!

Hey again! Yeah, what you're describing sounds exactly like what I dealt with on my BMW 5. The timing of your symptoms, showing up after 20 minutes of driving, that's pretty much identical to what I experienced. The fact that you've got a new battery but still having these issues really points to the sensor being the culprit. When I had this problem, my battery was also fairly new, which is what made it so frustrating. The workshop explained that the battery sensor is crucial for the car's charging system, it tells the alternator how much charge the battery needs. When it fails, it can send wrong signals, making the car think the battery's dying even when it's perfectly fine. Just a heads up based on my experience, while you're at the workshop, have them check the alternator too. In my case, they found the alternator was fine, but it's worth checking since the symptoms can be similar. The sensor replacement sorted everything out for me, no more warning lights, strong starts, and normal lighting since then. Let me know how it goes at the workshop. I'm really curious if it turns out to be the same issue!

Thanks so much for all this detailed info! Just got back from the workshop today and you were spot on, it was indeed the battery sensor causing all the trouble. They did exactly what you suggested and checked the alternator too, which turned out to be working perfectly. The mechanic showed me the faulty sensor and explained how it was sending incorrect readings to the system. Got it replaced and wow, what a difference! No more warning lights, the starts are strong again, and all the electrical systems are working normally. Cost was pretty similar to what you paid too. Really grateful for your advice about getting it checked quickly. Having this sorted gives me such peace of mind. Thanks again for sharing your experience, it helped me feel more confident about what needed to be done!