This is probably on this forum somewhere, but I sure can't find it, so... Can anybody explain what the differences are between the "A", "B", "C", and so on battery versions? How many different versions are there? I've seen references to "D", but that's it. Does Tesla make these distinctions, or are they categorized by the owner community, or...? When my Model S arrived in a few months, how do I tell what version I got? Thanks!