BMW M3 Terminal 30 & Battery Issues: Diagnosis Help

I have some experience working on cars, and I faced a similar issue with my 2003 BMW M5 last year. The symptoms were exactly like yours, battery warning, hard starts, and electrical gremlins all over. After struggling with it for a few days, I took it to my trusted workshop. Turns out the battery was completely shot and wasn't holding charge properly. They did a full electrical diagnostic and confirmed the battery was the main culprit, not the Terminal 30. Got it replaced for about 290 Euro, and it's been running perfectly since then. Just to be thorough, what's the mileage on your M3? Also, have you noticed any other electrical issues like flickering lights or radio problems? Knowing these details would help narrow down if you're dealing with the same problem I had. I've also owned a BMW 540i, so I'm quite familiar with how these cars can be when electrical issues pop up. Let me know the details and I'll try to help further!

Thanks for sharing your experience! Mine's at 66989 KM, just had the service done last month. I've actually noticed the radio occasionally cutting out, and the headlights do seem a bit dimmer than usual, especially at idle. The voltage meter also fluctuates a bit when I'm running the AC. I was hoping it wasn't the battery since it's only 2 years old, but after reading your post, maybe I should get it tested anyway. Did your battery also die gradually, or was it more of a sudden failure? These electrical gremlins are really starting to get annoying!

Hey again! Thanks for those details about your M3. You know what's interesting, your symptoms are actually really similar to what I experienced with my M5. My battery also was only about 2.5 years old when it started acting up, which is why I initially dismissed it as the cause. But these performance cars can be pretty demanding on batteries, even relatively new ones. The way my battery died was pretty gradual, started with small things like the radio cutting out (just like yours), then the headlight dimming, and finally those annoying voltage fluctuations. The AC thing you mentioned? Had exactly the same issue, every time I turned it on, the voltage would drop noticeably. Since you've got the same symptoms I had, I'd definitely recommend getting the battery tested ASAP. Even though it's only 2 years old, there could be a cell that's gone bad, or it might not be holding the right charge capacity anymore. The test is usually pretty quick and inexpensive, way better than being stranded somewhere! Just a heads up, when I replaced my battery, I made sure to get one with the right specs for these performance models. They need a bit more juice than standard batteries. The improvement was night and day, no more dimming lights, stable radio, and rock-solid voltage readings. Let me know what you find out after testing. If it turns out not to be the battery, we can explore other possibilities, but I'd put money on this being your issue.

Thanks so much for all this detailed info, it's super helpful! You've actually made me feel a lot better about the whole situation. I was dreading some major electrical system overhaul, but a battery issue seems much more manageable. I've already called my mechanic and scheduled a battery test for tomorrow morning. You're totally right about not risking getting stranded, that's the last thing I need! The way you described your battery's gradual decline matches my situation perfectly. Looking back, I probably ignored those early warning signs longer than I should have. I'll definitely take your advice about getting a higher-spec battery too. Better to spend a bit more now than deal with these issues again in another couple of years. Really appreciate you taking the time to share your experience. It's saved me a lot of worry and probably some money too! I'll update you once I get the results from the battery test.