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.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
President of CT/Westchester Section