Actually that doesn't remove the ignition switch or the starter from the list just because it starts when jumped off.

That's one thing that took my awhile to figure out the ignition switch was bad on my x5. I had forgotten the symptoms I had with the ignition switch on my e46 being about the same but since I knew the e46 had a good battery and knew the x5 had a bad battery or at least weak I figured it was all battery on the x5 with the starting problem I was having.

When the voltage was down to 12.2 or lower it would not crank at times. All the symptoms of a bad battery. If the voltage was 12.3 and above it always cranked.

The ignition switch was bad. Once the ignition switch was replaced it would crank just fine even down at 11.8 volts.

As for the starter a bad starter that's dragging and drawing to many amps will make a battery look bad by only successfully cranking when jumped. It used to be a much more common problem in the past than it is now but a bad starter (as in failing) can cause the same issues.

The ignition switch is simple to diagnose once you have experience with it on a bmw. If you turn the key and the lights come on but NOTHING happens when you try to start it and you have at least 11 volts its the ignition switch. That's kind of broad diagnoses wise and with any other car I wouldn't lump it in like that but so far its been the cause on about 8 different bmw's I have fixed by changing the switch out. I mean it could be security related blah blah blah but so far its been dead on with the ones I have worked on that were running fine then went out.

__________________
Just BMW's - All cars and trucks was two pages long
1994 318is
1997 528i
2000 323i
2001 X5 3.0 auto
2005 X5 3.0 auto
2011 535xi auto
2013 X5 xdrive35 Turbo
More are at my website

Aftermarket E53 Radio Install