A battery system comprising: a battery circuit group in which a plurality of battery circuits connected in parallel, each including a plurality of battery units (11a-11e) connected in series, each including a positive electrode end (113a-113e), a negative electrode end (114a-114e) and a battery (111a-111e); and a control unit adapted to determine a charge state of the battery (111a-111e), wherein each of the battery circuits has a diode connected in series with the plurality of battery units (11a-11e) such that a discharge direction of the battery (111a-111e) is a forward direction, wherein each of the plurality of battery circuits further includes a bypass switch connected in parallel with the diode, and; characterized in that each of the plurality of battery units (11a-11e) further includes a switching unit (112a-112e); the control unit is adapted to control the switching unit (112a-112e) based on the determined charge state, wherein in each of the battery units (11a-11e), the switching unit (112a-112e) is adapted to switch a state of the battery unit (11a-11e) between a first state, in which the battery (111a-111e) is connected between the positive electrode end (113a-113e) and the negative electrode end (114a-114e), and a second state, in which the positive electrode end (113a-113e) and the negative electrode end (114a-114e) are connected without the battery (111a-111e), wherein during a discharging process of discharging of the battery circuit group, the control unit is adapted to control the switching unit (112a-112e) such that the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being not fully discharged becomes the first state, and the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being fully discharged becomes the second state, wherein the control unit is adapted to control the switching unit (112a-112e) such that when charging of the battery circuit group, the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being not fully charged becomes the first state, and the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being fully charged becomes the second state, and wherein the control unit is adapted to control the bypass switches such that only one bypass switch of the battery circuits is turned on, and to control the bypass switches so as to sequentially charge the plurality of battery circuits by controlling the bypass switches such that the bypass switch in the battery circuit in which the bypass switch is on is turned off when it is determined that all the batteries (111a-111e) in the respective battery circuit are fully charged. a battery circuit group in which a plurality of battery circuits connected in parallel, each including a plurality of battery units (11a-11e) connected in series, each including a positive electrode end (113a-113e), a negative electrode end (114a-114e) and a battery (111a-111e); and a control unit adapted to determine a charge state of the battery (111a-111e), wherein each of the battery circuits has a diode connected in series with the plurality of battery units (11a-11e) such that a discharge direction of the battery (111a-111e) is a forward direction, wherein each of the plurality of battery circuits further includes a bypass switch connected in parallel with the diode, and; characterized in that each of the plurality of battery units (11a-11e) further includes a switching unit (112a-112e); the control unit is adapted to control the switching unit (112a-112e) based on the determined charge state, wherein in each of the battery units (11a-11e), the switching unit (112a-112e) is adapted to switch a state of the battery unit (11a-11e) between a first state, in which the battery (111a-111e) is connected between the positive electrode end (113a-113e) and the negative electrode end (114a-114e), and a second state, in which the positive electrode end (113a-113e) and the negative electrode end (114a-114e) are connected without the battery (111a-111e), wherein during a discharging process of discharging of the battery circuit group, the control unit is adapted to control the switching unit (112a-112e) such that the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being not fully discharged becomes the first state, and the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being fully discharged becomes the second state, wherein the control unit is adapted to control the switching unit (112a-112e) such that when charging of the battery circuit group, the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being not fully charged becomes the first state, and the state of the battery unit (11a-11e) including the battery (111a-111e) determined as being fully charged becomes the second state, and wherein the control unit is adapted to control the bypass switches such that only one bypass switch of the battery circuits is turned on, and to control the bypass switches so as to sequentially charge the plurality of battery circuits by controlling the bypass switches such that the bypass switch in the battery circuit in which the bypass switch is on is turned off when it is determined that all the batteries (111a-111e) in the respective battery circuit are fully charged.