BMW i4 Battery Drain Mystery: Help Needed

Hey there! I had some experience with a similar issue on my 2021 BMW iX3 (I also owned an i3 before). I've got some experience working on EVs, but I mainly trust professional mechanics for electrical problems. Last winter, my iX3 showed the same symptoms, rapid battery drain when parked and those annoying flickering lights. Turned out it was a faulty battery sensor that wasn't reading the charge levels correctly. Took it to my regular workshop, and they diagnosed it pretty quickly. The repair set me back 315 Euro, but it fixed the problem completely. Before you assume it's the same issue though, could you share: How long does it take for the battery to drain? Are you seeing any specific error codes? When did this start happening? This info would help figure out if you're dealing with the same problem I had. These BMW EVs are great, but their sensors can be a bit finicky sometimes.

Thanks for the detailed response! I'm at 74842 KM and just had my service last month, so this issue is quite frustrating. The battery usually drains within 48 hours of parking, and I'm getting the "Vehicle electrical system fault" message. Started about two weeks ago out of nowhere. Really appreciate your insight about the battery sensor, that actually makes a lot of sense given my symptoms. I was worried it might be something more serious with the main battery pack. Going to schedule an appointment with my service center tomorrow to have them check the sensors specifically. Did your car also take longer than usual to power up when you'd try to start it?

Hey again! Yes, absolutely, my iX3 had that exact same slow start-up issue you're describing. It would take a good 15-20 seconds longer than normal to power up completely, which was super annoying. What you're describing sounds incredibly similar to what I dealt with, especially that "Vehicle electrical system fault" message, it's like déjà vu! With your mileage being around 74K, it's actually right around when these sensor issues tend to pop up. Mine started acting up at about 68K. I should add something I didn't mention before, before I got it fixed, I noticed the car would sometimes show incorrect charge levels too. Like, it would jump from 70% to 40% without any actual battery drain. If you're seeing anything like that, it's another clear sign pointing to the sensor issue. Just a heads up though, make sure they check all the sensor connections too. In my case, they initially just wanted to replace the sensor, but there was also a slight corrosion issue on one of the connection points that needed cleaning. Getting both dealt with at the same time saved me from having to go back again. Let me know how it goes at the service center. Really curious if it turns out to be the same problem I had!

Thanks so much for the additional info, and yes, I'm actually noticing those weird jumps in the charge level display too! Just yesterday it went from 65% to 35% in literally no time. Should've mentioned that in my first post. I really appreciate you sharing about the connection points too. I'll definitely make sure to mention both the sensor and possible corrosion to the service center when I take it in. Actually just got off the phone with them and managed to get an appointment for tomorrow morning. It's such a relief to hear someone else dealt with this and got it sorted. I was honestly stressing about potentially needing a whole new battery system, which would've been a nightmare. Will update you after the service appointment, fingers crossed it's just the sensor like in your case! The symptoms seem identical, so I'm feeling much more optimistic now. Thanks again for taking the time to share your experience. Really helped put my mind at ease!