The growing pollution in the environment and the negative shift in the global climate compel authorities to take action to protect the environment and human health. Transportation is one of the major contributors to this environmental decay. The harmful gases released to the air by the vehicles using petroleum fuel increase each day. One of the solutions is to make a gradual transition to electric vehicles. A major part of manufacturing an electric vehicle is to produce an efficient electric motor and battery for it. Reducing the manufacturing and operating costs of these components will result in reducing the overall costs of electric vehicles. In this study, a new Electric Travelling Salesman Problem with Time Windows (E-TSPTW) was proposed. The objective function of the problem is to minimize the required initial battery capacity of the electric vehicle. For this goal, a new energy consumption model considering the load of the vehicle was proposed with three scenarios. The proposed model was solved with a hybrid Simulated Annealing algorithm for all these scenarios. The performance of the proposed method was compared to the solutions found by a Mixed Integer Linear Programming model. The experimental results on the benchmark instances show that up to a 35% reduction in battery capacity is possible.