Repurposing retired electric vehicle (EV) batteries provides a potential way to reduce EV cost hurdles. Embedded in energy storage systems, second-life EV batteries could unlock the energy storage market and generate synergic value for the energy sector. From case studies with various stakeholders, this paper presents key factors that impact the market development for second-life batteries and explains why some stakeholders are more capable for the market diffusion. The results provide practical implications for both industrial players and policy makers.