Electric vehicle (EV) power sources with a wide variable DC output voltage, such as supercapacitors, cannot be connected directly to the motor drive of the EV power train. Therefore, the power train requires a high-efficient bidirectional dc/dc converter between the power source and the motor drive. There are many dc/dc converters that accomplish that function, however in EVs, simple topologies are commonly used due to its reliability and ease of control. This paper is focused on the design of interleaved bidirectional buck-boost converters which provide energy with high-efficiency, robustness, ease to control and high specific power transfer (W/kg). High specific power transfer is important in vehicular applications to make them lighter, faster and more efficient. The paper analyses a design methodology for converters in the range from 1 kW to 10 kW power transfers for different weight constraints. Based on that analysis, a model was extracted that gives an approximation of the efficiency and the optimal number of interleaved converters as a function of the power transfer (W) and weight (kg). This approximation is extremely useful for designers in order to obtain the maximum profit of the power source (supercapacitors).