The utilization, dimensioning and operation of hybrid battery systems in all-electric vehicles is addressed in this work. These hybrid battery systems consist of one high power and one high energy lithium-ion battery each. Besides a discussion of the advantages of such a hybridization on battery system level, an insight is given into the dimensioning of the system and related aspects. Moreover, major focus of this paper is dedicated to the energy optimal operation of the hybrid battery system. Therefore, two optimization methods are investigated and applied to the given system and control problem. First the global optimal control solution is derived via dynamic programming. Then a causal controller, which allows for a real-time applicable control of the system, is discussed. A stochastic model of a vehicle's drive missions is introduced and implemented within a stochastic dynamic programming framework. The obtained control laws are applied to vehicle simulations, which include a model of the drivetrain and vehicle chassis. The performance of the controllers is then compared to each other using three driving cycles and two vehicle classes. Finally the causal controller is validated in a hardware-in-the-loop test bench.