I agree with all the above, same thing happened to me last week in my 2002 330i. I went to fill up, turn the car back on, no juice. Got jump went to battery + to buy a new battery. The day after same thing happened again with the brand new battery inside, I though I was in a disco b/c all the dash lights were flickering. Anyway it ended it up being the alternator which BTW killed the new battery installed, but thank God they replaced it without question asked.

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X5 4.4
E46 M3 Vert