This paper presents a novel anti-idling system, namely, a regenerative auxiliary power system (RAPS) for service vehicles. Auxiliary devices, such as a refrigeration system in a food delivery truck, require the engine to idle for providing auxiliary power while the truck stops for loading or unloading. By electrifying auxiliary systems, a battery pack can supply the auxiliary load, thereby reducing engine idling. The main advantages of the proposed anti-idling system over existing technologies are the optimal design and optimal performance (smart charging strategy) which lead to lower overall cost and less fuel consumption. The size of the components in the proposed system is optimized by a multidisciplinary design optimization approach to meet the conditions of compactness, modularity, and ease of installation. By introducing the anti-idling system to a service vehicle, its powertrain becomes hybrid due to the addition of a battery pack. Therefore, to optimize the efficiency, a power management system is developed to decide when and how to charge the battery. This controller operates based on the duty cycle that can be obtained by the proposed prediction method.