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Thread: Another battery drain mystery

  1. #1
    Join Date
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    Another battery drain mystery

    Hello all,
    New member, first post. I bought my 2011 535i about a year ago and fortunately haven’t had many complaints, but this battery drain issue has me ready to run this thing off a cliff. I’ve followed dozens of battery drain posts here in this forum, watched hours of YouTube videos, and I still have the same problem but mine is still a little different.
    Same story, battery seems dead, will not start, I can open the hidden menu using the reset trip meter button, view the codes and read the battery voltage. Typically for my car, when this happens, the system shows 12.1- 12.3 volts when it decides to pull this stunt. I replaced the battery and from what I’ve learned, the battery sits with 12.3- 12.5 volts. Once connected, the system and alternator charge it to 13.5- 13.7 volts. The car requires 13.5+ to turn the starter and crank the engine. I wish I could remember where I found that source. Okay, I’ll jump start it. My battery uses 920 CCA so, it’s pretty heavy duty right? I’ve had a friend, neighbor, coworker, jump it off with their trucks, even an F250 diesel with a heavy duty battery like mine. Nothing. It may charge up so the system shows up to 13.1-13.4 volts but never has successfully jump started. Left it on trickle charger overnight, nothing. So, like I said, I’ve left it charging, nothing. O’Rielly’s tested it, yeah man, the battery is good, no problem. Jumping it didn’t work. So, I give up, let it sit, read forums, study, get angry and think hateful things about my car. Go out the next day and give it another try. I get in, push the button and, the dang thing starts right up! WTH!? Like nothing ever happened. Voltage shows 13.6- 13.8 volts but the night before was 13.2-13.4? Does it somehow charge itself? I’ve gone over everything again and again and I can’t find anything. So does this car just decide to take a day off or what? “Hey dude, we’re not going anywhere today” Okay car, that’s fine but we can schedule this right? Yes, I talk to this car like this because it drives me crazy.

    Bottom line, sorry for the kind winded rant. The battery drain remains a mystery. I’ve read dozens of posts from you guys and mine seems a little different so I just wanted to share. Feel free to share your thoughts and opinions. What could I be missing?

  2. #2
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  3. #3
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    Quote Originally Posted by psychobimmer View Post
    The car requires 13.5+ to turn the starter and crank the engine.
    That's absolutely incorrect. A good, fully charged battery should be in the neighborhood of 12.6 volts. I've seen weak and worn out batteries below 11 volts still crank an engine (although slowly). With the engine off, you will never see over 12.6 volts. Once the engine is running, the alternator is now running, and supplying power to the vehicle. The normal range can be anywhere between 13v and 14.5v depending on electrical loads, condition of the battery, etc.

    It seems to me like you've done a good job of eliminating the battery as the culprit. I can just about bet you the starter is on the way out.
    ASE and BMW Master Certified Technician

  4. #4
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    I would believe it to be the starter if it would actually try to turn over. You are right though about the ignition off being around 12.6 volts and the idle voltage range being 13- 14.5, at least from what I’ve studied thus far. Of all the times it has done this, it will never start unless the system shows at least 13.5. Once it’s running, yes, it’s usually 13.5- 14.5ish. I’m thinking it could be the alternator but once the car decides to run again, it will do fine anywhere from a week up to a month before this episode happens again. If the alternator were consistently failing, I would think the battery wouldn’t hold a charge that long? An alternator replacement would certainly be easier than chasing this ghost of an electrical problem.

  5. #5
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    So again, after two days of the car sitting dead, it started this morning. No jump, no charger, it just started. White94RX mentions the starter... maybe the starter solenoid is not getting the proper amount of power to open and engage the starter? There hasn’t been any engagement of the ignition or starter so I just can’t make sense of how sometimes it works and sometimes doesn’t?

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