EcoCAR 2: Plugging in to the Future (EcoCAR) is North America's premier collegiate automotive engineering competition, challenging students with systems-level advanced powertrain design and integration. The three-year Advanced Vehicle Technology Competition (AVTC) series is organized by Argonne National Laboratory, headline sponsored by the U. S. Department of Energy (DOE) and General Motors (GM), and sponsored by more than 30 industry and government leaders. Fifteen university teams from across North America are challenged to reduce the environmental impact of a 2013 Chevrolet Malibu by redesigning the vehicle powertrain without compromising performance, safety, or consumer acceptability.During the three-year program, EcoCAR teams follow a real-world Vehicle Development Process (VDP) modeled after GM's own VDP. The EcoCAR 2 VDP serves as a roadmap for the engineering process of designing, building and refining advanced technology vehicles. During the first and second years of EcoCAR 2, teams executed an Energy Storage System (ESS) design, integration and commissioning process. The end result of the process is a functioning ESS that meets the technical specifications driven by the vehicle powertrain that is integrated into teams' competition vehicles.This paper gives a detailed overview of the EcoCAR 2 competition and the design and integration activities undertaken during the first and second year of the competition, while also looking forward to the final year. Specific focus is given to the ESS design and commissioning process and the overall outcomes of the process. As examples of how teams executed the process, four teams outline the design decisions made when sizing their ESS, designing their ESS thermal management system and any challenges that were overcome during the integration of the design. Additionally, overall competition results are presented and correlation between competition results and ESS selection is explored.