Abstract: The power supply device of an embodiment includes a first storage battery connected between a positive electrode terminal and a negative electrode terminal; a second storage battery connected in parallel with the first storage battery; a first switch that switches connection between a positive electrode of the first storage battery and the positive electrode terminal; a second switch that switches connection between a positive electrode of the second storage battery and the positive electrode terminal; and a battery management device that controls opening and closing of the first switch and the second switch, wherein energy density of the first storage battery is equal to or greater than energy density of the second storage battery, and wherein the first switch is normally closed and the second switch is normally open.

Abstract: According to some embodiments, a battery control device has a current detector, a storage, and a state determiner. The current detector detects a current value of a current which flows into a second battery which is connected in parallel to a first battery. The first battery and the second battery are charged with a fixed current. The storage stores an initial value of the current which flows into the second battery if the second battery is charged with the fixed current in an initial use stage of the second battery. The state determiner determines a state of the first battery based on the current value detected by the current detector and the initial value stored in the storage.

Abstract: According to some embodiments, a battery control device has a current detector, a storage, and a state determiner. The current detector detects a current value of a current which flows into a second battery which is connected in parallel to a first battery. The first battery and the second battery are charged with a fixed current. The storage stores an initial value of the current which flows into the second battery if the second battery is charged with the fixed current in an initial use stage of the second battery. The state determiner determines a state of the first battery based on the current value detected by the current detector and the initial value stored in the storage.

Abstract: A fuel cell having a plurality of stacked single cells in each of which an electrolyte layer is held between an anode and a cathode and between which a separator is interposed, wherein the electrolyte layer includes a sheet for holding the electrolyte containing, as the main component thereof, fine powder having a function of holding the electrolyte, and reinforcing ceramic fiber disposed in the sheet for holding the electrolyte to substantially run parallel to the surface of the sheet for holding the electrolyte.