[EuroSpec27]

Since I purchased my 2008 335i coupe (CPO), I had a problem with the battery. I would constantly get the "increased battery discharge" warning upon startup and have to reset my date/time. At first, I thought maybe the car sat on the lot too long and the battery just needed a good recharge. However, after commuting to and from work (1 hour) every day for several weeks, the problem persisted.

I notified the dealer, and they told me to bring the car in for a diagnostic. Everything appeared to be ok and "normal", so they did not replace anything and I went on my merry way. The problem seemed to go away after that visit, for a few months at least, but just as I was coming out of my CPO warranty, it happened yet again.

This time around, I said screw it and purchased a brand new OEM battery and had my friends over at ACM install it. Once again, everything worked great for months with no warnings, however the other morning upon startup, the dreadful message appeared yet again.

Now, my question is, what the hell could be causing my battery to drain out like this? I drive my car every day, and this is a brand new battery here, how could it already be dying? I've had the same two batteries on my boat for over 10 years now without a single problem, yet this damn BMW one won't hold a charge.

Could it be that I leave my iPod plugged into the Y-cable and in the car at all times? I am absolutely baffled here and don't know what to do. Any helpful info would be greatly appreciated.

Thanks in advance!

[cdgatti]

DO you know if they coded and registered the new battery?

[ctuna]

Google Parasitc battery drain e90.
There are many threads telling you how to isolate
a parasitic drain. But first
Check Alternator charging voltage.
New does not always mean good so another battery check
may be in order.
The car will draw about .5 amps when awake and
20ma when asleep. Could be not going to sleep do to
a lot of reasons.

electical e90 pdf
http://www.google.com/url?sa=t&rct=j...,d.cGU&cad=rja
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU

A code read with a BMW capable scanner is always a good first step.

[Wongway]

Might very well be a good example of why we're advised to get new batteries coded to the car.

If you put in a new battery without resetting the charging profile, the car's computer would still think the old battery is in it and continually try to overcharge the battery thereby shortening its life.

[EuroSpec27]

The new battery was coded to my car, so that rules that issue out. I'm thinking something isn't "going to sleep" when I lock my doors. But what could it be? And how can I pinpoint it? This is such a pain in the ass to have to deal with every day.

[GoRomeo]

Originally Posted by EuroSpec27

The new battery was coded to my car, so that rules that issue out. I'm thinking something isn't "going to sleep" when I lock my doors. But what could it be? And how can I pinpoint it? This is such a pain in the ass to have to deal with every day.

Your battery needs to be registered. Coding is needed if battery has diferent specs from the original.

[ctuna]

Although battery registration may effect the long term life of
the battery I don't think it effects short term problems so much.
OP already said he bought the factory battery and registered it.
Retest new Battery.
Check alternator output Voltage
then check how much current its drawing in the sleep mode.

[EuroSpec27]

Update: Had a few techs look at my car and the battery appears to be "fine", however I still get the warning every day or so. What the hell is draining this thing and how can I stop it?!

[6spdcoupe]

How did the techs look at the car ? Did the test the battery (isolated) and the alternator ? Load test ? Like others have said, that is where I would start. From there, then check for parasitic drains.

Finally, I would check/change your voltage regulator. The alternator could be fine, but with the regulator not so fine you would experience the Exact same issues that you are.