The power coupler in a Southern California Edison / DEMI Zinc-Air powered Chrysler research minivan is detailed including circuit theory, performance and road testing experience. A coupler is defined here to mean an electrical device which connects two different power sources together such that each source can individually contribute its optimal power characteristics. The power coupler connects long operating range Zinc-Air batteries with peak power (acceleration) NiCd batteries in a battery-battery hybrid configuration. This circuit could also be used in a motor generator -battery hybrid, and with various battery types. The power coupler uses a single 18 kHz IGBT (Insulated Gate Bipolar Transistor) switching circuit to provide main vehicle cruise power to 12 kW from the Zinc-Air battery at 95% conversion efficiency. When power demand exceeds 12 kW the difference is made up by the NiCd pack.When vehicle power demand is below the Zinc-Air batteries' maximum rate, the power coupler manages float charging of the NiCd pack. The power coupler circuit is also used as a low, medium and fast charger of the NiCd batteries from 110 V to 240 V ac power.Although the power coupler is capable of 20 kW continuous operation, it weighs under 8 kg (17.6 lbs) and occupies less than 4 liters (6 x 4.5 x 9 in) due to its high speed switching transformerless design. The power coupler circuit is in development at DEMI with technical assistance from Motorola Semiconductor, Inc.