Power supply unit having plurality of secondary batteries

A power supply unit comprising:

• a power generator that generates power;
• a first battery being charged with the power generated by the power generator and electrically connected to a first load and a second load, the first load requiring power higher than that of the second load, the power generator, the first battery and the first load being included in a first circuit, the first battery having a terminal voltage Vc(Pb) when being charged and a terminal voltage Vd(Pd) when discharging;
• a second battery that is electrically connected in parallel to the first battery, being charged with the power generated by the power generator, having higher output density or higher energy density than the first battery and electrically connected to a third load, the second battery and the third load being included in a second circuit, the second battery having a terminal voltage Vc(Li) when being charged and a terminal voltage Vd(Li) when discharging;
• and
• a switching means that is electrically connected between the first circuit and the second circuit and which switches between conduction and blocking between the first circuit and the second circuit, wherein
• the switching means is configured by a plurality of semiconductor switches being connected in series, each semiconductor switch having a parasitic diode connected in parallel to a switching element thereof, respective parasitic diodes present in the semiconductor switches face opposite directions where current flows, the respective parasitic diodes each having an anode and a cathode and respective anodes of the parasitic diodes being connected to each other, and
• the first battery and the second battery including respective terminal voltages satisfying a relationship expressed by:
• Vc(Li)<Vc(Pb);
• and
• Vd(Li)>Vd(Pb).