This paper presents a design methodology for a dc-dc power conversion system (PCS) for battery packs. The methodology provides with an optimal design of the PCS and the associated inductive-capacitive filter interfacing the battery pack with the PCS. The PCS adds superior capability over conventional designs, which is performing current and voltage perturbations at the battery terminals for the so-called electrochemical impedance spectroscopy (EIS). This technique is an option for battery state-of-charge (SoC) and state-of-health (SoH) assessment. The design is optimal in the sense that it minimizes volume and system power losses. Such multi-objective optimization is addressed adopting the theory of weighted sum and Pareto front. The methodology is tested through a case study, addressing a lithium-ion battery pack. The offered analyses permit to identify the impact in system performance of diverse design variables such as dc-link voltage for the PCS and its switching frequency.