BMW MY08 X5 Battery Problem

[Doug Huffman]

Field current increase will also increase alternator output.

I there any downside to frequent/regular external charging properly done? E. g., make sure the IBS can see the charge.

[lanbrown]

RTFM. i.e. it was what BMW recommends.

[koolkat1973]

I've noticed that my alternator takes about 30 seconds for it to kick upon start of the car. Is this normal for the X5? In my other two cars, the alternator kicks on immdiately upon startup. Thanks.

[lanbrown]

Yes, that is also part of this design. In other vehicles, the alternator cannot be decoupled, on a BMW they can.

[koolkat1973]

Thank you for the clarification.

[heatmizr]

Ok I bought a Jebsen voltmeter/car charger thingy as in the first post on this page, after all the worry on here and XBimmers. I am finding that the voltage displayed on there shows as follows:
-At start I sometimes see 11.9 but only for under 5 seconds. Then right up to 14.1-ish idling
-On the gas it shows anywhere from 12.3 - 14v, but for the vast majority of the time it is in the 14's.
-Coasting I don't see anything different than the above
-I have seen it show 11.9v once or twice, briefly

I haven't seen a correlation of lower voltage when on the gas, vs higher when coasting, BUT its hard to say because the main issue is that this device doesn't show Voltage continuously, it rotates between Voltage, Amps and Temp (useless info). Each is displayed for about 8-10 secs, so it is really hard to catch it on the V reading when driving a certain way to see if it varies.
I also can't tell if there is any delay in the readout, or if it is really real-time. I have seen it change while the V reading is displayed. So it may be real time.

I have only had it for a few days, and its hard to remember which voltages I saw match to what kind of acceleration/deceleration at that moment. However I can say that I am not seeing anything in the way of chronic low voltage readings. Some write-ups on this issue make it sound like the battery is not being charged much of the time, and I don't think that is the case. It may still be an issue overall, but I virtually never see it read under 14v.

I will continue to monitor and update this post if I can state my findings any more accurately.

Only thing I can state definitively is that if you are considering purchasing this thing, DON'T! Find one that displays Voltage and only voltage, all the time.
-Todd

[heatmizr]

Update to the previous post:
I had my battery replaced under warranty a couple months ago, I wasn't seeing any practical issue but the Jebsen was showing as low as 10.9v on startup for a few secs, until it rose to 13-14v. Actual voltmeter readings were only ~12 v at the battery terminals.
Anyway, the readings while driving above using the Jebsen all show similar but a few tenths of a Volt higher with the newer battery; 14.1v is now mid-14v...