Battery is draining overnight

I seem to be having an inordinate amount of trouble lately. But thanks to forums like this I at least have a shortcut to diagnosing these issues. Here is the latest:

Just replaced alternator and battery checks out. Car drives great and alternator actually solved rough idle, but now if the car sits overnight it will not start. Battery is 100% dead. Now this is happening only 50% of the time, the other 50% it cranks with no issue whatsoever. Any thoughts???

Also my alarm has been going off randomly and I am told the sensor under hood can be disabled with ease; anybody know where that is???

And btw the alarm is not what is draining the battery, I don't set it at night..

Thanks!!!

2005 745i with 74k

Was the alternator new or refurbished ? Did you check the charging system ? Was battery replaced recently ? If the battery was replaced at one point, was it properly registered ?
IMO...You need to get these things straightened out first. Did your car go to sleep within 30 minutes or so after the key removed ? After that you might wanna do a draw test. Good luck.

I don't have answers to many of the issues you raised. I don't know what the charging system is other than an alternator and the alternator was refurbished but has been tested since installing. And with regard to registering the battery, would this need to be done due to changing the alternator, and how is this done, and would this cause a drain if it isn't registered properly? Thanks for your response, I appreciate your advice. And you have a great looking 7.

Originally Posted by Beaug30

I don't have answers to many of the issues you raised. I don't know what the charging system is other than an alternator and the alternator was refurbished but has been tested since installing. And with regard to registering the battery, would this need to be done due to changing the alternator, and how is this done, and would this cause a drain if it isn't registered properly? Thanks for your response, I appreciate your advice. And you have a great looking 7.

For info the Battery must be registered to the car if it's been changed ....this is done at the stealers via the OBD connector beside the drivers door......OR via INPA software on a laptop with an adapter cable you can buy.


The Battery is controlled and monitored by the 'Power Module' fitted in the car.

The Power Module controls the following functions:

Power module functions

* Optimised charging
* Reduction of load-side peak consumption
* Shut-down of auxiliary consumer units
* Quiescent current monitoring
* Distribution mode
* Automatic electrical system isolation
* Load deactivation
* Electronic circuit breakers
* Central battery voltage notification
* Heated rear window (demister)
* Interior lights
* Boot lid and fuel filler flap control
* Data memory
* Fail-safe characteristics
* Check Control messages
* Diagnosis

Battery replacement

When a Battery Replacement is done this informs the Power Module of a battery change. The following operations are performed:

* The battery capacity is reset depending on the seasonal temperature.
* The current kilometre reading is stored.
* The stored battery statistical values (current, voltage, battery charge state) are deleted.
* The stored temperature statistical values are deleted.


So basically if the Battery hasn't been registered then the Power Module will still think the old battery is still fitted as it hasn't erased the old battery statistical values and updated it with the new battery values.

Now you're asking too many questions, also...lol The charging system can be checked or tested with or by the Voltmeter while the car is running, you would use the black lead/cable to connect to the any chasis ground of the car and the red lead/cable to the red jumper terminal in the engine compartment/under hood. No, you don't have to register the battery if you only replaced alternator. How old is your battery ? Either the battery doesn't hold charge or the alt. doesn't do its job by charging the battery. Or perhaps there's a draw somewhere in the car or the car doesn't go to sleep at all.
Providing more info can get you better answers, remember that.

Originally Posted by TechFreak

For info the Battery must be registered to the car if it's been changed ....this is done at the stealers via the OBD connector beside the drivers door......OR via INPA software on a laptop with an adapter cable you can buy.


The Battery is controlled and monitored by the 'Power Module' fitted in the car.

The Power Module controls the following functions:

Power module functions

* Optimised charging
* Reduction of load-side peak consumption
* Shut-down of auxiliary consumer units
* Quiescent current monitoring
* Distribution mode
* Automatic electrical system isolation
* Load deactivation
* Electronic circuit breakers
* Central battery voltage notification
* Heated rear window (demister)
* Interior lights
* Boot lid and fuel filler flap control
* Data memory
* Fail-safe characteristics
* Check Control messages
* Diagnosis

Battery replacement

When a Battery Replacement is done this informs the Power Module of a battery change. The following operations are performed:

* The battery capacity is reset depending on the seasonal temperature.
* The current kilometre reading is stored.
* The stored battery statistical values (current, voltage, battery charge state) are deleted.
* The stored temperature statistical values are deleted.


So basically if the Battery hasn't been registered then the Power Module will still think the old battery is still fitted as it hasn't erased the old battery statistical values and updated it with the new battery values.

Great job, TF. As always...Very informative. Thank you...my friend.

Originally Posted by Beaug30

I seem to be having an inordinate amount of trouble lately. But thanks to forums like this I at least have a shortcut to diagnosing these issues. Here is the latest:

Just replaced alternator and battery checks out. Car drives great and alternator actually solved rough idle, but now if the car sits overnight it will not start. Battery is 100% dead. Now this is happening only 50% of the time, the other 50% it cranks with no issue whatsoever. Any thoughts???

Also my alarm has been going off randomly and I am told the sensor under hood can be disabled with ease; anybody know where that is???

And btw the alarm is not what is draining the battery, I don't set it at night..

Thanks!!!

2005 745i with 74k

If it were me i'd change the battery and get it registered and see if the faults go away....or you could be on a wild goose chase ....

Originally Posted by TechFreak

If it were me i'd change the battery and get it registered and see if the faults go away....or you could be on a wild goose chase ....

+1.

Originally Posted by Beaug30

Just replaced alternator and battery checks out. Car drives great and alternator actually solved rough idle, but now if the car sits overnight it will not start. Battery is 100% dead. Now this is happening only 50% of the time, the other 50% it cranks with no issue whatsoever. Any thoughts???

Also my alarm has been going off randomly and I am told the sensor under hood can be disabled with ease; anybody know where that is???

The battery and alternator go hand in hand; if you just had a reason to replace the alternator, there is a pretty good chance that your battery will be dying or shot by now as well, and your symptoms kind of support that line of thought.

The hood sensor / switch is a pretty cheap part, and is the little switch just in front of the driver's side microfilter, along the top of the engine firewall, just toward the engine from the driver's shock tower. You should be able to just unplug it to test whether this is your issue.

when your alternator goes bad it can kill your battery. also i have a question do you have comfort access? if yes have that checked out

Thanks guys. All is very helpful. In an unusual piece of good luck the problem has righted itself, leading me to believe that the battery did not have enough time to fully charge or perhaps is on its way out. So I will change out soon and follow the registration process. Thanks Again.

Did you have any luck? My battery drains every so often. Something is draining it, but it could be the TCU, but I have yet to check it yet. Until then, I purchased a BMW battery charger and charge my battery regularly to keep it charged.

U could click the battery on low reserve this will do two things. Cut the power faster at night to a low drain. Second it will prove u have something keeping car on at night. Batter saith is in trunk open bettery cargo area look it says
reserave on or off. Push it foward. Until u get a new battery.