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Hi All

I drove about 30 miles last week having never had any issues with my 335d starting previously and when I got to my destination I turned the car off for 5 minutes before trying to start it to go home, but the battery was dead.

I had no previous warnings and have had none since. However, having jump started the car it had no problems getting me home and the return journey gave the car enough of a charge to start again for the next day or two. However, a the battery was then flat again and having never had this problem before I took it to my approved BMW dealer who found no problems with the battery or alternator, and he checked that the car was going to sleep properly so we can't work out why the car won't hold a charge having been fine for the last year I have owned it.

We put a new battery on the car yesterday and when starting it this morning it only just managed to start so I am fully expecting to have the same problem tonight when I try to start it to get home from work.

Has anyone else experienced this problem that could offer some suggested ways of sorting it out?
 

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I don't think you mentioned what year the car is.

I don't think you mentioned what year the car is.
If its 5 to 6 years old its normal to replace the battery .
Also it should be registered if new and the same type.
I would measure the voltage with and without the motor running.
It should be 12.6 without the motor running and around 14.5 with the motor
running . If you have a parasitic draw on the electrical system you need
to monitor the current draw and it's abnormally high disconnect stuff till
you find the bad circuit . If its like the gas powered car then the draw will be
around .5 amps with the car awake and 20 ma with the car asleep.

http://www.bawarec.ru/manuals/3er/e90/manuals-3er-e90-12.pdf

Also try putting a charge on the battery and see how long it lasts.
An elm327 bluetooth module and the torque amp can allow you to monitor the battery
voltage and I believe graph it.
Try locking the car every time this will put it in sleep mode quickly.
You didn't install any aftermarket equipment did you ?
30 miles is not very much and were they highway miles .
Maybe you need a battery tender such as a ctek3300 or better.
 
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