Charging circuit on anything newer than 98 is not going to go through the cluster. Possibly even as far back as the intro of the e36 and then e39... so maybe 92 and 95 respectively.

Have they tested the alternator while it is in the car? That's how I have them test... load test it. Then confirm the result with a multi-meter.

Just had to swap out a couple of alternators on my old 4.4i and they had a hard time even testing it accurately. OEM had bad voltage regulator, first rebuilt replacement (oreillys had same issue), and finally the second rebuilt one works great... but strangely enough still tested bad with his load tester on the vehicle. He said he can't test that alternator off the truck. So I had him grab a multimeter (I have one at home but didn't bring it) to verify voltage was steady at 14-14.5 volts.

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2005 X5 4.4i Build 04/05 Maintenance/Build Log
Nav, Pano, Sport (Purchased 06/14 w/ 109,000 miles) (Sold 8/15 w/121,000 miles)

2006 X5 4.8is Build 11/05 Maintenance/Build Log
Nav, DSP, Pano, Running Boards, OEM Tow Hitch, Cold Weather Pckg (Purchased 08/15 w/ 90,500 miles)

2010 X5 35d Build 02/10
Nav, HiFi, 6 DVD, Sports Pckg, Cold Weather Pckg, HUD, CAS, Running Boards, Leather Dash, PDC, Pano (Purchased 03/17 w/ 136,120 miles)