I drove my Dad's 528i on a 2000-mile trip once, and the day I got back, about an hour after I finished unpacking I went out to start the car and it wouldn't start. I couldn't believe the battery could be dead because it had been operating perfectly the whole trip...but it was it. I spoke to an honest BMW tech, and he said just to get the battery from AutoZone or from Batteries Plus (which actually carries the same brand of battery used in your BMW, just not with the BMW sticker on it). As it was, I don't have a Batteries Plus here, so I just got a new battery from AutoZone for about $70, dropped it into the car, and it worked perfectly. You can return it, so that's the best route to take before you start paying for expensive diagnostics.
Anyone who ever buys used cars online, anyone even THINKING of starting a "Is this deal too good to be true?" thread, anyone who wants to be more educated about protecting themselves must <a href='http://www.carbuyingtips.com/fraud.htm' target='_blank'>read this</a>.
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