Electrical energy storage could play a pivotal role in future low-carbon electricity systems, balancing inflexible or intermittentsupply with demand. Cost projections are important for understanding this role, but data are scarce and uncertain.Here, we construct experience curves to project future prices for 11 electrical energy storage technologies. We find that,regardless of technology, capital costs are on a trajectory towards US$340 ± 60 kWh−1for installed stationary systems andUS$175 ± 25 kWh−1for battery packs once 1 TWh of capacity is installed for each technology. Bottom-up assessment ofmaterial and production costs indicates this price range is not infeasible. Cumulative investments of US$175–510 billion wouldbe needed for any technology to reach 1 TWh deployment, which could be achieved by 2027–2040 based on market growthprojections. Finally, we explore how the derived rates of future cost reduction influence when storage becomes economicallycompetitive in transport and residential applications. Thus, our experience-curve data set removes a barrier for further studyby industry, policymakers and academics.