Batteries are the heart of an electric vehicle, so this thread is for discussing the Rivian design. The company uses the same pack for both the R1T and R1S, of course. The cells inside are cylindrical 2170s. This is the same dimensions found in the Tesla Model 3 pack though from a different supplier. According to this article, they are quite likely double-stacked, which helps them create packs that can hold so much energy -- 180 kWh in its largest pack. This other article goes into a little more detail, including some discussion of the pack's carbon composite shell and a “ballistic shield" and how it's cooled and heated.