The hybrid energy storage system (HESS), which combines the functionalities of supercapacitors (SCs) and batteries, has been widely studied to extend the batteries' lifespan. The battery degradation cost and the electricity cost should be simultaneously considered in the HESS optimization. However, the continuous decline in the price of lithium batteries may weaken the effectiveness of HESS, as the battery degradation cost becomes less important. This paper analyzes the influence of different temperatures and battery prices on the integrated optimization of HESS, including the optimization of SC size and energy management strategy (EMS) for electric vehicle (EV) applications. Based on an average temperature, the HESS performance is examined considering a wide range of battery prices (from $143/kWh in 2028 to $257/kWh in 2018). Simulation results show that both the SC sizing and EMS optimization results are robust to the temperature and the battery price. In addition, the total cost of HESS for customers is shown to be 12% less than a battery energy storage system, even at low battery prices. The HESS is therefore validated to be effective in EV applications in the near future. (C) 2018 Elsevier Ltd. All rights reserved.