Just get yourself a trickle charger.

BMW will categorize you as being a battery abuser and won't cover the failure.

Your warranty / maintenance docs say you need to drive 10 miles or so each day.

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Laser
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2011 535i Black Sapphire Metallic, Sport, Euro Del (ret)
2009 328i Black Sapphire Metallic
2007 Honda S2000 Berlina Black