I'm at almost 12 yrs and over 190k miles on the OE alternator.

I ALWAYS operate the X with a cigarette plug voltage meter, and swap out the battery when the meter reads 12.3 volts after sitting 8hrs. A tired battery will cause alternator failure sooner.

Just did the battery swap 2 days ago.

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'03 X5 4.4 Sport, last of the M62s (8-03 build date)
I believe in deadication to craftmanship in a world of mediocrity!