BMW E90 Battery Woes: Complete Electrical System Failure Help

Hey there! I have some experience working on BMWs. Had a similar issue with my 2011 BMW 5 series (had it before switching to a 7 series). Had exactly the same symptoms, dead battery, weak lights, and those annoying error messages. Turned out it wasn't just the battery itself, but a faulty battery sensor that wasn't reading the charge levels correctly. My mechanic diagnosed it pretty quickly and replaced both the sensor and battery. Cost me about 315 Euro total, but it fixed all the issues completely. Before you head to the shop, could you share: Current battery age? Are you getting any specific error codes? Does it happen more after short trips? This could help narrow down if you're dealing with the same issue. Feel like we might be looking at similar problems here, but let me know these details and I can share more specific info from my experience.

Thanks for the detailed response! I've got 22778 KM on my car since my latest service, and yeah, this battery is actually the original one from 2009 (I know, I know, probably should've changed it earlier). Not getting any specific error codes, but the symptoms are exactly like what you described with your 5 series. And yes, it's definitely worse after short trips, sometimes won't start at all if I've just made a quick run to the store. Really appreciate the tip about the battery sensor. That's not something I would've thought to check. Might be worth looking into both issues since my battery's so old anyway. Did your mechanic mention how common this sensor problem is with BMWs?

Hey again! Yeah, after seeing your mileage and especially hearing that it's the original 2009 battery, I'm even more convinced it's similar to what I dealt with on my 5 series. These BMWs can be pretty sensitive with their electrical systems. When I had mine, the mechanic actually told me these sensor issues are pretty common in BMWs from that era. Mine started acting up around 15 years in, but honestly, I was lucky it lasted that long. The sensor basically tells the car's computer how much juice the battery has, and when it goes bad, it confuses the whole system. The short trip thing is exactly what happened to me too, it's because the battery isn't getting enough time to recharge between starts. With a faulty sensor, the charging system doesn't work properly, making the problem even worse. Here's what worked for me: got both the battery and sensor replaced at the same time. Made sense since the battery was old anyway. After that, all those annoying symptoms disappeared completely. The car started running like new again, no more weak lights or error messages. Just a heads up, if you're planning to replace the battery, make sure they register the new one with the car's computer. These BMWs need that extra step, something I learned the hard way when I tried to do it myself first!

Thanks so much for all this detailed information! You've honestly made me feel a lot better about the whole situation. I was worried it might be something way more serious (and expensive), but this sounds pretty straightforward. It's actually kind of a relief to hear these sensor issues are common, at least I'm not alone! Definitely going to get both the battery and sensor replaced together. Really appreciate the tip about registering the new battery too, that's exactly the kind of thing I would've had no clue about. My car's definitely earned a proper fix after all these years of reliable service. Think I'll book it in at the shop tomorrow. Hoping my bill comes in around what you paid, seems pretty reasonable for both parts and labor. Thanks again for taking the time to share your experience, this is exactly the kind of real-world advice I was looking for!