While cleaning the battery posts and the terminals I noticed a slight spark when I returned the hookup. My?

question is that should there be a slight drain on most of these newer computer controlled cars as a normal thing? It is a 2005 sentra. In the past as I recall going back to model 'A' Fords and 1948 chevrolets there should not be a steady drain with everything off. The 48 chevy had an electric clock that only drew off a small insignificant amount of battery, I disconnected it as it never kept time anyway. Also as the hood was in the 'up' position I checked for a trouble light as well as any door ajar.