You may want to disconnect the battery. I have heard that there could be a trickle discharge over time. I'm not sure how long "over time" is but, it's just something that I heard.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member