BMW M2 Battery Warning Nightmare: Sensor or Cell Issue?

Hey there! I had nearly identical issues with my 2015 BMW M4 last year. The battery sensor was indeed the culprit. When I brought it to the garage, they diagnosed it as a faulty intelligent battery sensor (IBS) that was sending incorrect readings to the car's computer. Initially, I also thought it was just the battery, but the symptoms matched exactly what you're describing, dim lights, rough starts, and those annoying warnings. The mechanic explained that when the sensor fails, it can't properly monitor the battery's charge state, causing the system to freak out even when the battery is fine. It took about two hours to fix, they replaced the sensor and recoded the new one to the vehicle. While it wasn't a major repair in terms of complexity, it's definitely something that needs proper attention since it affects the whole electrical system. My battery itself was actually in good condition and didn't need replacement. If you're getting the same symptoms, I'd definitely get the sensor checked first before replacing the whole battery.

Thanks for sharing your experience! That's really helpful. This actually sounds exactly like what I'm dealing with. Really good to know it wasn't super complicated to fix. Just curious, do you remember roughly how much you ended up paying for the sensor replacement and coding? Also, has everything been running smoothly since the repair, or have you noticed any other electrical quirks?

Hey again! Happy to help with an update. Yeah, I remember you were dealing with pretty much the same issues I had. I actually just got everything sorted out, had the sensor replaced for 315 € total (parts and labor), and I'm glad to report it fixed the problem completely! Since the repair, my M4 has been running like a charm, no more battery warnings, no dim lights, and those annoying sluggish starts are history. The mechanic definitely nailed it when they diagnosed the faulty battery sensor. All the electrical systems are working perfectly now, just like they should. I know it's a bit of cash to drop on a sensor, but it's way better than unnecessarily replacing the whole battery or dealing with those constant warnings. Haven't had a single electrical quirk since the fix, which is such a relief. The car feels like new again, honestly. Sometimes it's the small things that can cause the biggest headaches, right? Let me know how yours turns out if you go ahead with the repair!

Thanks for the follow-up! Actually, I got my car fixed yesterday and wanted to share my experience. Turns out you were spot on! Took it to a new mechanic who specializes in BMW electronics. The whole thing was way less painful than I expected. The fix cost me around 350 for parts and labor, pretty close to what you paid. They had to replace the sensor and do some computer coding. The mechanic was super professional and even showed me the old sensor, explaining how it had failed. The difference is incredible! My car starts up instantly now, the lights are back to full brightness, and best of all, no more annoying warning messages on the dash. Been driving it for a day now and it feels like a completely different car. Really glad I asked here before spending money on a new battery. The mechanic even mentioned these sensors commonly fail around the 150-180k km mark, so it makes total sense. Thanks again for steering me in the right direction, saved me both time and money!