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      01-03-2013, 12:47 AM   #15
Private First Class
Jffeijao's Avatar

Drives: 2011 335d
Join Date: Nov 2012
Location: Luxembourg

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Originally Posted by Vreimann View Post
Actually from my experience over the Christmas break this is not true for the cabin controls and the temp was only -28 to -31Celsius.

I did my winter loop to visit family and over our 10 day winter break. On the first leg of trip the battery was frozen to the point where the car would start but not provide heat under the Auto or manual function. The voltage is too low, and the computer will not allow the fan to run in auto or manual.

The only way to keep the windows from frosting was to push the defrost setting which works fine to keep the front windshield from frosting up but you get no heat on your midsection or feet. Driving like this for many hours is not fun.

Needless to say there are additional items required to make this vehicle work in winter. -31 celsius was enough to freeze the battery to keep the fan function from working and it never really worked until the last portion of the loop where we lucked out and a Chinook system was able to warm the battery up to around -10 celsius.

Talking with the SA, this happens to be a common issue to when the temp drops.
With the engine running, electrical system's voltage shall be anywhere from12.5 to 14 volts. This is generated by the alternator and limited by a voltage regulator. Battery is not source of power, it is just an energy acumulation device. In your case, if engine starts, the battery is not the cause of your issue. It might be something else in the electric system of the car.
I agree that under extreme low temps the battery performance dramatically decreases, as the chemical reactions that enable charge/discharge are severely impacted on their dynamics. So heating the battery would enable faster energy replenishment.
The other potential cause is the overall power consumption at a given circumstance being above the alternator's capacity. This is unlikely but possible and would drain energy from the battery with eventual malfuctions on electricity dependant features. This could stall the car when the battery capacity reserve is drained. You would not be able to re start the engine without help.
2014 X5 30d M
2011 335d
2012 Grand Cherokee (sold!)
2003 MB SLK stick (garage queen)