No. Just disconnect the negative lead. With one disconnected there is no path for current to flow from the battery to any components/computers. The negative lead is the one recommended to be disconnected if only removing one (or first, if disconnecting both). This is a safety measure. If you attempt to disconnect the positive lead from the battery first and accidentally short your wrench between the positive terminal and any exposed metal - you will get a large and powerful arc. By disconnecting the negative lead first (or only) the exposed metal of the vehicle will be at the same potential (same voltage) as the positive terminal. The only danger of the electrical arc at that point is if you actually short out the battery posts with your wrench.Should I have done both?