Oftentimes research papers on batteries will mention the capacity and the resulting energy density of a battery system in the background, but I'm confused how the theoretical energy density is calculated given only the capacity information of the anode and cathode. For example, Li and S is 3860Ah/kg and 1685Ah/kg respectively, how do we get 2600Wh/kg for the Li-S battery if energy density=nominal voltage x cell capacity and the cell runs at 2V? And when we use Na as the anode (1166 mAhg1), Na-S batteries has a theoretical energy density of 1274 Wh/Kg, how so?