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Hei, i own 2006 bmw 525d with universal body. After close to 6 months of worm weather we hit -4 and suprise suprise, car won't start, no lights, no nothing full black out. and now when our weather is like 1-2°C then the car shows it only has 10.3v. I have LED lights in interior, When i let the car go to sleep mode and checked the A with multimeter, then it showed like 0.045A. Also i have one code for k-can but i don't remember the code(when i get home i will post it here). Also the big + cable from under car has been changed last year by bmw dealer.

Also last owner diy'd the air suspension in the back.

Any suggestions what i should look for?

Thanks!
 

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Hei, i own 2006 bmw 525d with universal body. After close to 6 months of worm weather we hit -4 and suprise suprise, car won't start, no lights, no nothing full black out. and now when our weather is like 1-2°C then the car shows it only has 10.3v. I have LED lights in interior, When i let the car go to sleep mode and checked the A with multimeter, then it showed like 0.045A. Also i have one code for k-can but i don't remember the code(when i get home i will post it here). Also the big + cable from under car has been changed last year by bmw dealer.

Also last owner diy'd the air suspension in the back.

Any suggestions what i should look for?

Thanks!
How old is your battery? Sometimes a bad cell won't show until it's extremely cold

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There will be some reduction in the voltage on an otherwise good battery due to very cold temperatures. FWIW, it looks like 25mV per degree C (that's .025 volts per degree C, or 14mV / 0.014 volts per degree F). That would mean less than a volt drop at the temperatures the OP mentioned. Even so, his measured voltage indicates one of several things...

1) The battery was not fully charged (maybe been sitting for days, or only driven for very short distances and never really properly charged). This happens with a bad / failing alternator or other electrical issue.
2) There could be a parasitic drain on the battery that's running it down overnight. Of course, the cold just makes it worse, or possibly, the problem causing the battery drain is somehow related to the cold weather. It sounds like this isn't the case, based on your readings (though some drains are intermittent - for an example, my rear glass hatch was self-triggering, turning on my interior lights, which would run my battery dead overnight once ever few months).
3) The battery is somehow toast already (hard to imagine in less than a year, but it's not unheard of).

At any rate, your battery should be registering close to 12 volts even when it's near 0°C (32° F). If it's not, AND it's being properly charged (around 14 volts with the car running), then it sure sounds like the battery is getting flaky.
 

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some of these cars will try to keep the cabin heated while you are away. that sucks battery down. make sure you don't have that option and if so, make sure its not enabled. I would think it would only run until water temp reaches certain temp, but it could be faulty.
 
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