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Steve, BMW Expert
Category: BMW
Satisfied Customers: 25232
Experience:  BMW Expert
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My E70 intermittently drains it battery in hot weather. I can

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My E70 intermittently drains it battery in hot weather. I can tell when it's doing it as when sitting with no key in the ignition, locked or unlocked, it makes a sound like it's trying to activate the central locking. I've had it checked 3x by an auto electrician but because it's intermittent, he's not been able to locate the root cause. Now I carry a booster pack for when the battery is flat.
The car is a 2010 30D Sport with 41000 miles. Any ideas to help me?
It is difficult to know how to answeer general requests for "ideas"
Can you please be more specific about what type of info you are seeking?
Customer: replied 3 years ago.
I want to trace the fault which is causing the battery to drain and get it fixed. The warning about increased battery discharge can appear within 2hours of driving the car and it has drained completely several times this summer.

I will provide an honest answer. I trust this will be appreciated on a sunday. Please remember that a low rating PUNISHES me for being honest and that I receive nothing for my time until a positive rating is clicked.

normally if you get this warning the first step in diagnosis should be a scan for faults using a factory BMW diagnostic computer. The car has a lot of on board systems to help ferret out issues like this, and making a small investment in a proper diagnostic can save liiterally hours of manual testing trying to trace an initermittent issue that is not present.

if you do not wish to invest in proper testing, to test manually for an electrical drain you will need to - with the issue present - diconnect the vehicle batter and hook up an amp meter

then you will need to spoof the car so it thinks all doors and trunk/boot are closed, wait 30min for the car to go into sleep mode, then start pulling fuses one by one while monitoring amperage draw. whatever fuse stops the drain is the problem circuit

the most common causes are a faulty nav computer, fan controller or engine fan, but the issue could be ANYTHING on the car including the battery sensor

again, this is difficult testing to carry out, especially on this vehicle given its complexity. BMW has engineered computer diagnostics for this type of issue, and this would be the preferable route.

Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle

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