Couple things:

Alternator:
- Bosch 120A AL0703N is about $200 new.
- Valeo: 120A vs 140A...about $300 new.

I'd NOT touch a rebuilt alternator from local store.

Battery:
- Best bang for the buck is Exide L3, about $90 at Menards or Home Depot.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT