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Robert, BMW Technician
Category: BMW
Satisfied Customers: 4340
Experience:  Fully qualified 19+yrs exp/self employed technician in the UK
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735i runs battery down when not used for two weeks. Isthere

Customer Question

 2002 735i runs battery down when not used for two weeks. Is there a battery capacity issue with this car?


The car is is excellent condition 69000 miles from new. new electric controller. All working correctly. no problem starting engine if in regular use.




Submitted: 2 years ago.
Category: BMW
Expert:  Robert replied 2 years ago.



Hopefully i can help..


You should also consider if the battery is the same from new and as far as your aware the battery hasnt been changed at any point - could well point to the batttery itself has exceeded its lifespan..usually most batteries have life span of upto 5-6 years before they start to give problems.a load test on the battery should test to see what condition its in..most garages will have that certainly something to bear in possible too you have slow drain on the certainly check for aftermarket installations on the car that could be drawing power when the car is way to know that is to check the electrical draw the battery has on it when the car is locked up, with the key in the "off" position". and the doors locked wait 15 minutes roughly, then disconnect the battery cable on the negative/earth side. Attach a test light/ digital multimeter between the negative battery cable end and the negative battery terminal. The test light should illuminate extremely dimly or not at all. If the test light is on brightly or quite bright there is a sign there is an electrical draw in the system. To locate you will need to start removing and refitting fuses "one" at a time so you'll need to be careful which ones you pull so you'll need to refer to the manual each time or the lid and start of with the known ones first in particular as far as the fuse(s) for those bulbs/lights and work your way through them and keep referring the the testlight/multimeter etc to see any change. if or which ever fuse is removed and the test light goes out or voltage drops on multimeter the circuit in question has been located . You will need to identify that pulled fuse and what it covers within the car and that should be where the parasitic drain is on that circuit either a faulty component or a wiring fault on that particular circuit which will need tracing and investigated carefully...Also sometimes if cars are unused for period of time to prevent battery failure..dpending where the car is parked up ie:- in a secure garage or driveway - you can get these smart chargers to ensure the battery is always topped up if and when need again something else to consider..I do hope this helps

Customer: replied 2 years ago.

Thank you Robert, Not sure what you mean by electronic draw. Can you clarify please.


It has a lot of electronic equipment, some like the computer and security system will be operational all the time. As far as I am aware there is no additional equipment.

Expert:  Robert replied 2 years ago.

Hi..there thanks for your reply..


Electrical draw as in regards to something on the car drawing power when the car is unused..for example something on the car continually draining or has become faulty to cause that..maybe things like interior lights.glovebox light/boot light etc needs checked out..only the above test as per described would likely route that out..but certainly have the battery checked out al the same..i do hope this helps further

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