Abstract: A system includes a first DC rail configured to be coupled to a first terminal of a first energy storage device (e.g., a battery), a second DC rail configured to be coupled to a first terminal of a second energy storage device (e.g., an ultracapacitor), and a plurality of converter legs coupled between the first and second DC rails and including at least one first converter leg configured to be coupled to a second terminal of the first energy storage device and at least one second converter leg configured to be coupled to second terminal of the second energy storage device. The system further includes a switch configured to couple and decouple the second terminals of the first and second energy storage devices. The at least one first converter leg and the at least one second converter leg provide different current capacities to deal with differences in power density of the energy storage devices.