The present invention generally relates to an energy storage system and, more particularly, to an energy storage module to be incorporated into a hybrid electric motor vehicle to store high voltage energy. 
Over the past few years, there has been a growing concern over global climate change due to an increase in carbon dioxide levels as well as oil supply shortages.  As a result, some automobile manufactures and consumers are beginning to have a greater interest in motor vehicles having low emissions and greater fuel efficiency.  One viable option is a hybrid electric vehicle (HEV) which allows the vehicle to be driven by an electric motor, combustion engine, or a combination of the two. 
Though various features are important to the overall HEV design, the system which stores the energy available for use by the vehicle is a key component.  The energy storage system is provided within the HEV to store the energy created by a generator in order for that energy to be available for use by the hybrid system at some later time.  For example, the stored energy may be used to drive an electric motor to independently propel the motor vehicle or assist the combustion engine, thereby reducing gasoline consumption. 
However, energy storage systems face a variety of design complications, such as over-heating, weight, complexity, ease of incorporation into the vehicle, ease of service, and cost, just to name a few.  Additionally, known energy storage systems utilize only a specific and known number of battery packs or modules designed to meet a particular HEV design specification.  For example, a battery pack may be specifically designed to provide a specific amount of energy for a 300V vehicle.  However, when a different amount of energy is required, such as a 600V system, a different battery pack must be designed to meet the needs of that application.  Known battery packs and storage systems can not be utilized or otherwise implemented into different settings without a considerable amount of re-engineering and re-working. 
Some known systems allow for separate battery packs to be electrically connected to a separate and distinct control box.  Though the independent battery packs may be added to or removed from the overall system, the separate control box is still required.  However, because available space for HEV components is at a premium, the inclusion of a separate and distinct control box should be avoided.  Additionally, in the event the separate control box fails, the entire energy storage system is unable to function. 
Thus, there is a need for improvement in this field.