There are so many speculations about the Battery Day, that I have stop looking at them. Nobody of those guys, presenting videos on YouTube really knows, what Musk is going to present.

My own speculation, based on the behavioral pattern, is that it is going to be less significant, that these speculations suggests. Very likely, it is going to be a "Pumper Day" to cover up for worsening market situation of Tesla and pointing attention of followers to new area of hype. This time, it is going to be the “million miles” battery (which has been here for some time, just not used because of lower energy density) and an announcement of some proprietary Tesla battery. They may even go that far to announcement its own production (but in small volume, because Tesla is contractually obliged to use JV production)