For a series fuel cell hybrid electric vehicle (FCHEV), it is critical that the degree of hybridization between the fuel cell power and battery power be determined so as to maximize the vehicle's performance variables, such as fuel efficiency and fuel savings. Because of the cost of and wide range of design choices for prototype vehicles, a development process that can quickly and systematically determine the design characteristics of hybrid systems (including battery size and vehicle-level control parameters that maximize the vehicle's net present value [NPV] during the planning stage) is needed. Argonne National Laboratory developed AUTONOMIE, a modeling and simulation framework, and, with support from MathWorks, the laboratory has integrated that software with an optimization algorithm and parallel computing tools to enable that development process. This paper presents the results of a study that used the development process, in which the NPV was the present value of all the future expenses and savings associated with a vehicle. The initial investment in the battery and the future savings that will result from reduced gasoline consumption are compared. The investment and savings results depend on the battery size and vehicle usage. For each battery size at the given fuel cell power and efficiency, the control parameters were optimized to ensure the best performance possible from using the battery design under consideration. Real-world driving patterns and survey results from the National Highway Traffic Safety Administration (NHTSA) were used to simulate the usage of vehicles over their lifetimes.