Battery system for switching connection states of battery modules

1. A battery system comprising:

a plurality of battery modules;

a plurality of switches configured to switch a connection state of the plurality of battery modules between a series state and a parallel state, the series state being a state in which the plurality of battery modules is connected in series, the parallel state being a state in which the plurality of battery modules is connected in parallel; and

an electronic control unit configured:

to control switching of the plurality of switches; and

to stop switching ON-OFF states of the plurality of switches such that the connection state of the plurality of battery modules is the series state or the parallel state until receiving a cancel instruction from a user, in response to a deterioration parameter indicating a degree of deterioration of a predetermined battery module out of the plurality of battery modules reaching a threshold value, the ON-OFF state representing a state in which a switch is open or closed.

2. The battery system according to claim 1 , wherein:

the electronic control unit is configured to resume switching of the ON-OFF states in response to an activation of a fixing cancel switch by the user.

3. The battery system according to claim 1 , wherein:

the plurality of battery modules includes a first battery module and a second battery module;

the plurality of switches includes a first relay that is disposed on a first electric wire connecting a positive electrode of the first battery module and a positive electrode of the second battery module, a second relay that is disposed on a second electric wire connecting the positive electrode of the first battery module and a negative electrode of the second battery module, and a third relay that is disposed on a third electric wire connecting a negative electrode of the first battery module and the negative electrode of the second battery module;

a first node to which the first electric wire and the second electric wire are connected is located closer to the positive electrode of the first battery module than the first relay; and

a second node to which the second electric wire and the third electric wire are connected is located closer to the negative electrode of the second battery module than the third relay.

4. The battery system according to claim 1 , wherein:

the plurality of battery modules is configured to be able to be charged with electric power of a power supply outside the plurality of battery modules; and

the electronic control unit is configured to:

maintain or change the ON-OFF states of the plurality of switches such that the connection state of the plurality of battery modules is the series state when an operation for starting charging using the power supply has been performed in a situation in which the ON-OFF states of the plurality of switches continue switching; and

stop switching the ON-OFF states of the plurality of switches such that the connection state of the plurality of battery modules is the series state in response to the deterioration parameter reaching the threshold value while charging using the power supply is being performed or after the charging has been completed.

5. The battery system according to claim 4 , wherein the deterioration parameter is an inter-terminal voltage of the predetermined battery module when the charging has been completed.

6. The battery system according to claim 1 , wherein the electronic control unit is configured to stop switching the ON-OFF states of the plurality of switches such that the connection state of the plurality of battery modules is the series state when the deterioration parameter reaches the threshold value.

7. The battery system according to claim 6 , wherein:

the plurality of battery modules is configured to be able to be charged with electric power of a power supply outside the plurality of battery modules; and

the electronic control unit is configured to:

maintain or change the ON-OFF states of the plurality of switches such that the connection state of the plurality of battery modules is the parallel state when an operation for starting charging using the power supply has been performed in a situation in which the ON-OFF states of the plurality of switches continue switching and a voltage of the power supply is equal to or lower than a predetermined voltage value; and

stop switching the ON-OFF states of the plurality of switches such that the connection state of the plurality of battery modules is the series state in response to the deterioration parameter reaching the threshold value while charging using the power supply is being performed or after the charging has been completed.

8. The battery system according to claim 7 , wherein the deterioration parameter is an inter-terminal voltage of the predetermined battery module when the charging has been completed.