Thread: Bad Battery?
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      03-29-2013, 07:31 AM   #13
CUTigers
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Drives: 2008 Montego Blue 335i
Join Date: Mar 2012
Location: Atlanta/Lawrenceville

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2008 Lexus IS F  [10.00]
2008 e90 335i  [9.00]
Quote:
Originally Posted by mr_milo
Quote:
Originally Posted by fun2drive View Post
News Item
This isn't your old BMW or Audi. I assure you if you are in the short driving cycle your battery has most likely been killed or soon will be. The charging system in this car is ultra complex. I am an EE by training and this charging system doesn't just do alternator to voltage regulator then back off once the battery reseaches sufficient charge. No-no this has the intelligent battery sensor (IBS) which in and of itself is a microprocessor with sensors to measure the temperature of the battery itself, charge rate, cycles of use,cable temperatures (not kidding here). All of this goes to the DME for a State of Charge (SoC) and the DME tracks this which is called Statement of Health (SoH).

To say this is over engineered to improve battery life by maybe 15% is an understatement.

Main point
Can this issue with your battery cause the top to stop in cycle?
I don't know but our alternator on the 335 is a 180A alternator. I think it is possible.

How would you check this?
Do not rely on BMW here for your 2007 but go to a part store that has a load tester. This is nothing more than a bank of resistors that help load the battery down similar to loading the battery as you would with your top operation. If it fails the test your battery is toast.

For the 2011 I would let BMW do this and expect a report back that you are abusing the charging system by short use (it is actually in the manual about the battery insufficient charging with short trips). I would argue with your SA that they should replace the battery. You will get this done once but after that it is your issue.

Comfort Access?
I don't know. If you are talking about touching the door to lock and unlock I would say no. If you are talking about opening the top using the CA I would say possible for the reasons stated above.

Solutions
First LOCK YOUR CAR
No matter if in the garage or where ever locking the car puts the DME to sleep (but not the IBS by the way) and will reduce the milliamp load (which is killing your battery) by the DME not cycling on every 4 hours to check the health of the car.

Second
Buy either a Deltran Battery Tender (even a junior battery tender works fine) or a CTEK intelligent battery charger and use it when you don't drive the car. Say you are not planning to drive the car for a couple days use the charger.
You can install the wiring cable to the jump posts in the front of the car permanetly or just use the clips and leave them attached. I have done both for well over 10 years and it works very well.
This will help keep your battery topped off all the time and the short trips will not cause issues because you will keep it maintained.
My E93 was the 2nd Euro delivery in Apr 2007 (Mar 2007 manufacturer) and my battery is still fine after 6 years because of the battery tenders (Deltran or CTEK take your pick both are very good).

My battery is a 900AH AGM sealed battery by the way which is what yours should be as well unless BMW changed the batteries to another AH.

Hope this helps and please report back what you discover as we try to help as best we can but we don't always hit the mark. We all learn by your reports...
Thanks for the information but personally I think this is an over-engineering design flaw. I am an EE too and I've found a few over-engineered items which turn into design flaws on this car. It's basically too smart for itself and ends up being dumb when you try to use it. Now I totally understand why Jeremy Clarkson from Top Gear went off about the I-drive. I can also tell you for a fact that the Comfort Access & Opening the top with the fob will both turn off when the battery gets low. Problem is the functions just stop working and their is nothing telling you why they stopped working. Now that's an over-engineered design flaw. It's a shame too since it is a great driving car it just becomes not a great car to drive day to day.

My question would be this: How far must I drive to "maintain" the battery??? My commute is driving 9.7 miles each way to and from work. It takes me about 21 minutes each way with a mix of city streets and freeway for a total of about 19.4 miles / 42 minutes per day. I really don't consider this a "short" drive. I mean it's not like I'm driving to the corner store and back, but it seems it is too short for the BMW. Shouldn't I have been given a disclaimer about this when I bought the car?

The statements above basically tell me I need to sell my car since I can't use it for my driving needs without buying a new battery every two years or so. I didn't buy a "plug-in" and was honestly insulted when the SA told me "buy" a trickle charger and do so. If it needs it, shouldn't they be providing one? Personally I feel the same way about "locking" my convertible when the car is in my garage with the top down...... just another bit of dumbass over engineering in my book.

Lucky13 - Sorry to rant in your thread. I am just very upset about this battery BS on a $55K car. I do know that certain systems do start to shut down when the battery gets low. My top operation via the FOB almost never works anymore and I've even had comfort access shut down and not work. Once I had to try the remote button several times and was just about to resort to the actual key when it finally opened. And yes, the fob battery was new or at least less than 2 months old.
But a generic battery from a parts store that has a 3 or 4 year warranty and get it replaced when it does after 2, if that's how long yours are lasting.
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