FYI ... I believe my newer BMW battery will become discharge with our lite use of the X5 and I believe we can ruin a battery sooner this way. My plan .... I have showing up tomorrow a cigarette lighter "voltmeter" etc. called A "Jebsen 4in1 car charger" for $11.99 via Amazon. I will monitor the batter voltage with this! I will then fully charge the battery using a 021-0123 I already have for my boat.
And then I watch the voltage at rest. I suspect the x5 voltage will drop over weeks and as needed I will charge the battery weekly or bi-weekly? To make this easier I may need to install a plug in my x5 grill to go to directly to the battery "jump spot". At any rate ... I will not see the battery harmed or have the car ... strand me or my wife. I won't even let the X5 confuse me with failing systems because they aren't working right because of a low battery ... go figure.
I am a engineer this isn't rocket science but it isn't it just it works either! Shame on BMW for making such a stupid flawed design here!

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I do the same Ron07X5.

Cigarette lighter volt meter, smart charger if the X sits for more then 3 days.

I also replace the battery when voltage drops to 12.2 after sitting for 2 days.

12 yrs/200k miles and still on OE alternator, OE battery lasted 8 yrs, Autozone battery 4 yrs, just installed a Bosch unit.

BMW is not alone here, a lot of brands have issues when vehicles are not driven far enough to charge the battery. There have been a huge surge in adding in electronic features that all suck down power. The alternators have not increased in capacity to match. BMW went a more complicated route but getting 4.5 years out of a battery is about what you would expect. Ford, GM, Chrysler ll have had battery issues as well. There are many modules in the car and they all take power and they usually have an awake and a sleep mode. When they are awake, they take more power and it can be 30 to 45 minutes before they go to sleep. The battery a car has today is not much different than the battery they had over 20 years ago.

I think a 48-volt system will help things. You can use thinner wires as they can handle the same wattage compared to a 12 volt system. Say you need 48 watts on a 12 volt system. That would be 4 amps and would require a 15 AWG wire. On a 48 volt system, that would only be 1 amp and a 21 AWG wire can be used. A 48 volt system could help reduce power requirements; the hybrids aren't using 12-volts motors.

Another factor that has caused this; more gears. We have had four speeds for ages and then 5 speeds came around, then 6 speeds and not long after 7 to 10 speed transmissions. The reasoning has been better fuel mileage and how do you get better fuel mileage with more gears? Reduce the RPM while driving. In the city and not going fast enough for top gear; you will still find an 8 speed allowing lower RPM's than say a 6 speed. On the highway, you will find an 8 speed allows lower RPM's for going the same speed. Lower RPM's means lower alternator output since it to is spinning slower. Add more electronics in a vehicle that want power and you have to drive farther to replace what was consumed by the starter and the electronic while it was off.

The N63 has a 230 amp alternator. The N62 has an 180 amp alternator. Both of those ratings would be at 2500 RPM or higher. I can be in top gear and run at around 1000 to 1100 RPM doing around 45 to 50. On a 6 speed, that would be about 1300 RPM. To go 70 MPH; it is 1900 RPM on an 8 speed and 2100 RPM on a 6 speed. So while the alternator is larger, it has to be because the engine is spinning slower to do the same amount of work.

There are many factors why people are seeing battery issues now compared to earlier vehicles.

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.

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

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.

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

Thank you for the clarification.

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