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Discussion Starter · #1 ·
I have E39 M5 with nav,phone and DSP.
If I leave the car parked for approx 6-7 days without starting it, the battery will be dead. It jump starts very easily though.
BMW have put in a new battery 6 months ago but no difference.
They have done a drain test and say nothing is wrong.
I am in the UK so it is not very cold.
Is this normal?

Moderator Emeritus
2,977 Posts
No that is not normal. The dealer is BS-ing you.

How did they perform the drain test?

There are two methods, one of which works:

A. Disconnect battery. Connect mA current meter eletrically between battery and car. Read total current out of battery.

B. Don´t touch the battery connections. Clamp a magnetic current sensor
around one of the battery cables. Read total current out of battery.
Then proceed to clamp the sensor around individual wires at the fuse-panels until the culprit load is found.

Method A is useless, as it will cause a reset of all electronics. When the current drain is too big it is usually because of an error that will disappear for a while after such a reset, only to re-appear later.

Method B is highly effective, as it will not upset the malfunctioning electronics, and it will pinpoint the problem.

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