Alternator at 70k miles is not "normal" wear & tear. Battery might.
What kind of an X do you have? the 3l or the 4.4l?
Seems like there is a flurry of 3l with shot alternators lately. Not sure why.
Personally I own an e39 with the M54B30 engine, and I have no problem with the original alternator. There are numerous e39 owners that have NOT changed the alt, and they have significant higher mileage than I have - some getting close to 200k or over.

It "might" have something to do where the X is build. The e39 were built in Germany - hence German Bosch alternator (or Valeo) throughout the life cycle. The X is built in USA and they have the Mexican Bosch alternator. Maybe this is the reason why

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Stable: e92is, e46 M54B25, e83 N52, e53 N62 - sold, e39 M54B30 R.I.P.