Won't run without battery connected...

[slowlanemcvane]

I can speak on this matter myself, having recently (within the last 18 months) replaced the alternator on my wife's 2007 X5 4.8i (4-zone, of course).

It definitely points to a bad alternator, but as said above, never, never, NEVER disconnect a battery from a running car built much more recently than 10 years ago. The electronics and electrical systems are a lot more sensitive and fragile than they were in cars even 15 years ago.

I replaced the alternator on my wife's car, with a brand new Autozone alternator. I got mine for $150 out the door, and it has given me 18 months and 20,000 miles of flawless, silent operation. I don't know what year your car is, but none of the parts retailers in my area had the high-amp alternator for the 2007, so the tech at the Autozone (normally, tech and Autozone is mutually exclusive, but this guy knew his stuff) looked at 2008+ X5, and came up with a compatible part that fit and worked exactly as the OEM part did.

Cheers.