I had talked to an expert employee of BMW about the heating of the i8. He told me that for the heating of the interior also the engine heat of the internal combustion engine is used, not only the electric heating, which is fed by the battery. When the i8 is cold and is going off, the electric heating immediately acts, fed by the battery. So it is warm very fast, but the small battery also has to supply a lot of power for it, so that it loses so very quickly total capacity. before I present the heating at the lowest level (16 degrees, automatic air conditioning) in case of cold. The first time I drive in sport mode, so that the combustion engine gets temperature as quickly as possible in order to fire the interior heating. If the combustion engine is warm enough, I set the temperature up as I would like it to be. I turn off the sport mode. So I try to save the battery as efficiently as possible. ll supply the burner, not the battery. It is also possible otherwise, easy to drive and let the car heat as quickly as possible, powered by the battery. Charge the battery permanently with the sport mode. But I think it is not very efficient.