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      03-14-2013, 02:38 AM   #21
martin mustang
Second Lieutenant
 
Drives: 2011 520, X3 & 88 635csi
Join Date: Apr 2011
Location: Ireland

Posts: 295
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Quote:
Originally Posted by raleedy View Post
The key battery is not involved in starting the car. That's why the car still starts when the key battery is dead. But the battery helps you get in your car, so keeping a spare battery in the car is problematic.

Not sure I agree with you on this one, if you try to start the car with key a good distance from it the car will refuse to start, therefore I think the system in place is down to signals between the two, but you manage to start the car with the battery dead (not able to open the car) because the signal needed to open the doors is a lot stronger than the one for the engine start, hence the option in the manual to put the key against the steering Colum due to the weak signal, this to me make sense since also a battery is never completely dead, a tiny energy will always still be around just on the weak side to complete the task.
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