Battery failure
 

The answer to this may be fairly obvious but here goes…
Circa 6 months ago I was sitting in the X5 4.4 with the radio on for 10 min or so and when I went to start up the battery was flat. Got the wife to bring me a spare from our Range Rover that I had in the garage so I put that in and drove home.
Put the ctek on it.
All very good. Been on the car since.
Regularly have the ctek on as I only usually do quite short journeys.
Yesterday the same thing happened. Again 10 min with the radio on and battery was not powerful enough to turn the starter.
This time I’ve put that other spare from our motorhome in.
Anyway, all 3 batteries have been fully charged up with the ctek and I’ve tested them all with my battery tester and it shows that they are ok.
Im going to buy a new one today but just thought I’d run this by you lot for something to think about.
More often than not the car has a bit of a long crank which obviously is not good for any battery but also I have noticed a sound in the dashboard kind of like a fan or motor running when the door is open but the key not in.
Is it possible that I have a faulty heater resistor that is allowing the fan to run slowly sometimes?
Is there a way to check it? My climate system works perfectly as far as I am aware.
Thoughts?

I’ve re tested the three batteries and they are ok. Just bought a FSR to swap out just in case…

Battery failure
 

FSU is the most common parasitic draw fault on e53. It can fail in a mode where it functions normally but draws power when off.

That said get a reading on current draw for the starter. When they start to fail they can draw up to double the current.

Next: you can have a battery fail in a weird way that it can deliver enough current to start the car but not have any capacity. The symptom exactly matches your description.

In my case 30 minutes of charging an iphone was enough I couldn't start the car and the final straw was that I ran the hazard flashers for about 8 minutes.

The car started just fine even multiple starts in a row including at 6°F, it also passed a cold crank test at batteries plus.

The battery should be able to run the flashers for hours and still start the car.

What tester did you use? Something like the 100A resistive tester? Like I mentioned my failed battery passed that test just fine. Put a modest load like 4A on it and watch voltage. 90ah battery should last 90/4=22.5 hr. If the battery loses voltage quickly it has suffered the same fate as mine.

My tester is one of those big load testers. All three batteries were in the green with a load on them so I don’t think it’s a faulty battery or it would show a difference between them.
I’ve got the car (with the spare motorhome battery) on the ctek until I use it next which will be Tuesday.
I’m also going to get a mini portable booster…

Look into parasitic draw but that aside see if you can run flashers for 30 min. and still start the car. Like I said my battery passed the load test but couldn't start the car after 30 min. charging an iphone. In your case with 3 batteries it pretty much has to be parasitic load

The heating/cooling controller unit (IHKA) has a small interior air sampling fan in there that runs when the car is awake. It's in behind the small left-side grill on the IHKA.

https://xoutpost.com/attachments/x5-...ka_sensors.png

You describe what I believe is my issue but I'm just not looking to spend a Benji to find out if it will fix it. OBC unlock shows mainly 13.2-13.6. If I decel to brake, or even start to idle, I'll see it dip to 12.2, even maybe as low as 12 for a quick second. I'm not sure if it's the alt. I have a weird issue with my trunk unlocking itself and then cycling the lock every few minutes......so if this happens, this drains the battery dead. Comes with the territory of a 21 age chassis

Once a lead-acid battery has been fully drained a few times, it's life and capacity are severely reduced. :(

They work (and last) best if kept close to fully charged at all times. Chemistry at work...

If your charging system is failing (a number of possible causes) and/or you have a faulty module causing parasitic draw, then battery death is imminent. :rolleyes:

Voltage should not dip add you describe. That's the main symptom of failing brushes on an alternator.

The brushes get higher resistance when they are end of life which will limit the current on the armature when it's needed most (idle). I replaced the brushes and brought a couple alternators back to life.

I cannot recall but will have to dig - when does the cluster show alt error. I suppose only when it's outputting constant too high or too low V.