A6 and S6 Sportback E-Tron electric cars arrive in North America next spring or summer The first cars using Audi’s new platform cut a sharp shape A 94.9-kwh usable battery pack supports three models The Audi A6 and S6 Sportback E-Tron join the Porsche Macan EV and Audi Q6 E-Tron SUVs as the first cars to utilize Volkswagen Group’s new…