If the alternator were failing it could have overwhelmed the battery and headlights if the headlights were on. But the poster makes it seem like a sloppy repair job so if ignition was on and headlights in AUTOMATIC mode when alternator or battery were being replaced then that.
Take a pic of loose wire. Was BMW using battery vent and hose in his 3-series ? Or were there any aftermarket alarms or stereos on the car?
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