A single energy storage technology will deliver either high power or high energy density. In high cycle applications like 48 V mild hybrid electric vehicles, lithium-ion batteries or supercapacitors have to be oversized to meet power, energy and cycle life requirements. However, a passive hybrid energy storage system is able to meet those challenges, but its performance depends on several factors. In this study, simulations and experimental investigations show how the design and operation conditions influence the performance of a passive hybridized system. In a comparative study for 48 V systems, consequences on performance are discussed.