A vehicle includes an engine cranked by an electric machine powered by a first battery, a first plurality of components powered by the first battery, a second plurality of components powered by a second battery, and a processor programmed to isolate the second battery and associated components from the first battery and associated components at least during engine cranking. The first battery may be a low voltage battery having a first chemistry, such as a lead-acid battery with associated components that are less sensitive to voltage variation induced by engine cranking or starting, such as heated mirrors, seats, wipers, a climate control blower, power windows/doors, and auxiliary pumps. The second battery may be a low or high voltage battery having a second chemistry, such as a lithium-ion battery with associated components that may be more sensitive to low voltage during engine cranking/starting, such as lighting, electronics, and infotainment systems.