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Discussion Starter #1
Wanted to make my first post about the battery drain I have been facing ever since purchasing my 06 m3 smg vert last October.

First things first I was told the battery was new, the sticker on the battery even confirmed this but since it was a cheap battery I went ahead and replaced it with a new AGM one from advanced after I let the car sit for two weeks and there was no life from the car. No lights no anything while trying to turn the key.

Fast forward another two weeks, the same thing happens with the brand new battery, I take it to advanced and they confirmed it was ok. Picked it up next day fully charged and installed it......about a week in I come home from work and the cars headlights, dash lights, stereo and rear lights are all on....Key is inside the house. I unplugged the battery and it was fine after plugging it back forward another week same ghost all the lights on issue happens again. I figured this was what was destroying my battery. After tons of research and doing many parasitic drain tests... I replaced the ignition switch hoping that this would fix the weird electrical issues based on my research not because the parasitic drain test pointed to it. After replacing that part the car has never had that happen again.... I figured that was the end of the battery drains.....Or So I thought.

I fully charged the battery and was driving the car regularly so I didn't notice any weird drains. I left it sitting for about a week while I was on vacation, I try and start it when I get back ....Click Click Click. Check the battery and it's sitting at 7v. I charge it back up and run parasitic test again multiple times ...the cars goes to sleep every single time and shows 0.01 amp draw after the 16 min sleep cycle. So I start charging the battery to full to see how much it's losing over night. On average the battery was losing about .4v every night. So I started doing research again and figure out the main culprits. FSR, bad radio, bad electric fan or bad diode in altenator.

I started to pull out all the fuses that pertained to these things and the drain kept happening. I knew it wasn't the radio because I had already pulled that out to install a new Avin head-unit. The alternator was working correctly to charge the battery so I left that as a last resort. I decided to attack the FSR, when I pulled it I noticed it was the original to the car from 06 so I was hopefull. While I waited for new FSR to come in I kept checking battery drain. The volts dropped had gone from .4v every night to just .2v....well at least that helped a little bit. I started messing with the electric fan and hood latch connections to make sure those were not causing it. The .2v drain kept happening, and on a whim I decided to message a buddy that is a master bmw tech to see if I was missing anything.

He sends me the same list I had of known culprits but with a new addition.....The BMW bluetooth/phone module that is in the trunk. I decided what could it hurt I don't need it anyways since my new head-unit has BT. I unplugged it from the trunk cables and just unbolted it instead of just removing the fuses...The battery was at 12v when I unplugged it....I go back three days later to install the new FSR (just wanted a new one just in case it was also the culprit, plus I had it out already and its a **** job.) I check the battery and it is still at 12v. What makes think this was the main issue is because when I had the original nav unit in the car none of the phone capabilities worked.

TLDR:CHECK THE BLUETOOTH MODULE IF U HAVE IT!!!! But also make sure you do an actual parasitic test. My issue was unusual because my tests were showing the car was going to sleep like it should ...but the battery kept draining.

I will update this thread after a couple of weeks to make sure everything is all good to go.
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