A power supply unit with improved charge/discharge operation for use in distributed
power supply system or electric vehicles. The power supply unit includes a storage
battery comprising a plurality of circuits connected in series. Each of the plurality
of circuits includes a first cell group and a second cell group connected in parallel.
The first cell group includes lithium secondary cells or electrical double layer
capacitors. The second cell group utilizes an electrolyzable electrolytic solution,
or is capable of generating recombinable gas. The second cell group may include
lead cells, nickel hydrogen cells, nickel cadmium cells and/or fuel cells. A charger/discharger
is provided for controlling charge/discharge of the storage battery adapted to
charge the storage battery up to a voltage at which the electrolytic solution of
the second cell group is electrolyzed, or to a voltage at which the generated gas
is recombined.
