The battery system is a main driver of current reservations against electrical vehicles, because it influences aspects like vehicle range, charging time and costs. Further the battery system is highly connected to the surrounding subsystems of the vehicle. Hence, developing battery systems means to deal with manifold interconnectivities. Within this, sufficient and transparent objectives for the battery system have to be defined. This work presents a systematic approach to defining objectives for the battery system down to the behavior of battery cells by considering the drive system in relevant use cases. Three investigations on the complexity of developing battery systems are done: Interviews with engineers to investigate the challenges of developing battery systems, parameter variation in a vehicle simulation model to analyze the influences of the surrounding systems and analysis of the theoretical interdependencies between battery system, power electronics and electric drive. The findings in combination with the literature research lead to requirements to be met by the approach. In addition to the battery system the configuratio ... mehrn of the drive system should be considered as well as different customer relevant use cases. An approach to defining objectives for battery systems based on a parameter variation is introduced and it is explained how concrete objectives can be derived from customer perceptions in a transparent way.