<p>Electric vehicles (EVs) and hybrid electric vehicles (HEVs) have gained popularity owing to their eco-friendly characteristics. However, the weight of the engine/generator in HEVs is a burden when used in the EV mode. Moreover, EVs have limitations regarding the charging/waiting time or driving distance. This study investigates a novel concept to overcome these disadvantages using energy packs, which can be manually attached and detached. According to the new system, the use of existing gas stations or electric charging stations is available, while charging during driving is also feasible. To maximize the efficiency of the proposed vehicle, we present core efficiency improvement factors, such as the target power of the engine and the required power of the motor. The efficiency of the proposed concept was evaluated through urban and rural driving cycles considering weekday and weekend scenarios; the efficiencies were compared with those of plug-in HEVs and EVs. As a result, remarkable enhancements in efficiency were demonstrated for the proposed system. In addition, the effectiveness of the efficiency improvement factors in the new system is demonstrated using the simulated annealing (SA) optimization technique to minimize the problem of total fuel consumption.</p>