METHOD FOR BATTERY MANAGEMENT AND BATTERY SYSTEM PROVIDING THE SAME

A battery system includes: a battery and a battery management system (BMS) for controlling charging of the battery depending on a normal mode using a first battery capacity between a first lower limit state of charge (SOC) and a first upper limit SOC or an eco-friendly mode using a second battery capacity between a second lower limit SOC and a second upper limit SOC, the first lower limit SOC is smaller than the second lower limit SOC, and the first upper limit SOC is greater than the second upper limit SOC.

TECHNICAL FIELD

Cross-Reference With Related Application(s)

This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0087773, filed in the Korean Intellectual Property Office on Jul. 15, 2020, the entire contents of which are incorporated herein by reference.

The present invention relates to a battery management method and a battery system for providing the same, capable of extending cycle-life of a battery.

BACKGROUND ART

An electric vehicle (EV) is a vehicle that uses an electric battery and an electric motor without using petroleum fuel and an engine. Such electric vehicles include pure electric vehicles (EVs) that run only with batteries and electric motors, hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

The electric vehicle mainly uses a lithium ion battery as a battery, and a 400 V driving battery and a 12 V auxiliary battery may be installed. The electric vehicles that are recently mass-produced and distributed in the market may travel up to 350 km on a single full charge (e.g., the Chevrolet Bolt EV), and this varies greatly depending on a vehicle type. Various modules/devices for user convenience in an electric vehicle consume power when driving, and thus may affect a mileage of the electric vehicle.

As a charging method for batteries, slow charging and rapid charging methods are selectively used. For such a charging time, it is known that slow charging takes 4 to 9 h and rapid charging takes 30 min to 1 h, and with development of battery technology, slow charging or fast charging speed is being improved. A charger charges electrical energy by connecting a charging cable to a charging terminal of an electric vehicle, and typically supports a high-speed or low-speed charging type.

In the meanwhile, after a predetermined period of time elapses, for example, when a predetermined number of charge or discharge cycles is reached, a battery capable of charging and discharging rapidly deteriorates in performance and needs to be replaced. In particular, such a replacement period of the battery may be shortened or lengthened depending on a usage pattern of a user. For example, there are many research results showing that the cycle-life of the battery is shortened as a number of 100% charging and discharging increases or as a number of times of charging by the rapid charging method rather than slow charging increases.

A ratio of a battery to the cost of an electric vehicle (EV) is about 40%, which is very large. When the cycle-life of the battery is shortened as aging is accelerated as overcharge or over-discharge of the battery is repeated, a problem arises that a replacement cost of the battery increases. This may act as a burden when a user purchases an electric vehicle (EV), and may eventually become an obstacle to each country's policy of environmental protection by expanding a number of electric vehicles.

Accordingly, there is a need for a method capable of extending the cycle-life of the battery depending on an environment in which the electric vehicle is used, a user's tendency, and the like.

DISCLOSURE

Technical Problem

The present invention has been made in an effort to provide a battery management method and a battery system for provides the same, capable of reducing a usable battery capacity, and charging a battery with a slow charging method when an eco-friendly mode (ECO MODE) is on.

Technical Solution

A feature of the present invention provides a battery system including: a battery; and a battery management system (BMS) configured to control charging of the battery depending on a normal mode using a first battery capacity between a first lower limit state of charge (SOC) and a first upper limit SOC or an eco-friendly mode using a second battery capacity between a second lower limit SOC and a second upper limit SOC, wherein the first lower limit SOC is smaller than the second lower limit SOC, and the first upper limit SOC is greater than the second upper limit SOC.

The BMS may calculate a current SOC by estimating a SOC of the battery every predetermined period, and in an on state of the eco-friendly mode, may start charging of the battery when the current SOC reaches the second lower limit SOC and may end the charging of the battery when the current SOC reaches the second upper limit SOC.

The BMS, in an on state of the eco-friendly mode, may disable a rapid charging method of charging the battery such that the current SOC reaches the second upper limit SOC within a predetermined reference time, and may control charging of the battery by using a slow charging method of charging the battery such that the current SOC reaches the second upper limit SOC after exceeding a predetermined reference time.

The BMS, in an on state of the normal mode, may calculate a current SOC by estimating a SOC of the battery every predetermined period, and may start charging of the battery when the current SOC reaches the first lower limit SOC and may end the charging of the battery when the current SOC reaches the first upper limit SOC.

The BMS, in an on state of the normal mode, may control charging of the battery by using a rapid charging method of charging the battery such that the current SOC reaches the first upper limit SOC within a predetermined reference time or perform a slow charging method of charging the battery such that the current SOC reaches the first upper limit SOC after exceeding a predetermined reference time.

The BMS, in an on state of the normal mode, may control the charging of the battery by the rapid charging method or the slow charging method depending on driver selection.

The BMS may determine that the eco-friendly mode is in an on state when receiving a key-on signal of the eco-mode depending on driver selection, and determining that the normal mode is in an on state when receiving a key-off signal of the eco-friendly mode depending on the driver selection.

Another feature of the present invention provides a battery management method for a battery management system (BMS) to manage a battery by controlling charging of the battery depending on a normal mode using a first battery capacity between a first lower limit state of charge (SOC) and a first upper limit SOC or an eco-friendly mode using a second battery capacity between a second lower limit SOC and a second upper limit SOC, the method including: determining whether the eco-friendly mode (ECO MODE) is in an on state; starting and controlling the charging of the battery when a current SOC that is estimated every predetermined period reaches the first lower limit SOC or the second lower limit SOC depending on a determination result thereof; and ending the charging of the battery when the current SOC reaches the first upper limit SOC or the second upper limit SOC, wherein the first lower limit SOC is smaller than the second lower limit SOC and the first upper limit SOC is greater than the second upper limit SOC.

The starting and controlling of the charging of the battery may include: diagnosing whether or not the current SOC reaches the second lower limit SOC when the eco-friendly mode is in an on state as a result of the determination; starting the charging of the battery by using a slow charging method of charging the battery such that the current SOC reaches the second upper limit SOC after exceeding a predetermined reference time when reaching it as a result of the diagnosis; and diagnosing whether the current SOC reaches the second upper limit SOC.

The starting and controlling of the charging of the battery may include: diagnosing whether or not the current SOC reaches the first lower limit SOC when the normal mode is in an on state as a result of the determination; starting the charging of the battery by using a rapid charging method of charging the battery such that the current SOC reaches the first upper limit SOC within a predetermined reference time or a slow charging method of charging the battery such that the current SOC reaches the first upper limit SOC after exceeding a predetermined reference time when reaching it as a result of the diagnosis; and diagnosing whether the current SOC reaches the first upper limit SOC.

The starting of the charging of the battery may include controlling the charging of the battery by the rapid charging method or the slow charging method depending on driver selection.

The determining of whether the eco-friendly mode (ECO MODE) is in the on state may include determining that the eco-friendly mode is in an on state when receiving a key-on signal of the eco-mode depending on driver selection, and determining that the normal mode is in an on state when receiving a key-off signal of the eco-friendly mode depending on the driver selection.

Advantageous Effects

According to the present invention, it is possible to extend a cycle-life of a battery by reducing use of upper and lower limit SOCs of a usable battery capacity and a number of rapid charges, which accelerates aging of the battery.

According to the present invention, it is possible to reduce a number of charges by using a maximum available battery capacity, and to increase user satisfaction by enabling a user to select a normal mode, which provides convenience in using a battery with a short charging time, and an eco-friendly mode, which extends a cycle-life of the battery, depending on a situation.

DESCRIPTION OF THE DRAWINGS

FIG.1illustrates a battery system according to an embodiment.

FIGS.2A and2Billustrate views for describing a normal mode according to an embodiment.

FIGS.3A and3Billustrate views for describing an eco-friendly mode according to an embodiment.

FIG.4illustrates a flowchart describing a method of extending cycle-life of a battery by charging the battery in a normal mode or an eco-friendly mode depending on user selection according to an embodiment.

MODE FOR INVENTION

In an embodiment, an electric vehicle indicates any vehicle that includes a battery and an electric motor for driving a wheel by using electricity charged in the battery. Such electric vehicles include electric vehicles (EVs) as well as plug-in hybrid electric vehicles (PHEVs). The electric vehicle may charge a battery with power supplied from a charging device that is electric vehicle supply equipment. The charging device may include a quick charger (or fast charger), a slow charging stand that supplies AC power in public places, and a home charger that is simply installed at home or at work to supply AC power.

Hereinafter, embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings. In the present specification, the same or similar components will be denoted by the same or similar reference numerals, and a repeated description thereof will be omitted. Terms “module” and/or “unit” for components used in the following description are used only in order to easily describe the specification. Therefore, these terms do not have meanings or roles that distinguish them from each other in and of themselves. In describing embodiments of the present specification, when it is determined that a detailed description of the well-known art associated with the present invention may obscure the gist of the present invention, it will be omitted. The accompanying drawings are provided only in order to allow embodiments disclosed in the present specification to be easily understood and are not to be interpreted as limiting the spirit disclosed in the present specification, and it is to be understood that the present invention includes all modifications, equivalents, and substitutions without departing from the scope and spirit of the present invention.

Terms including ordinal numbers (e.g., natural numbers) such as first, second, and the like will be used only to describe various components, and are not to be interpreted as limiting these components. The terms are only used to differentiate one component from other components.

It is to be understood that when one component is referred to as being “connected” or “coupled” to another component, it may be connected or coupled directly to the other component or be connected or coupled to the other component with a further component intervening therebetween. On the other hand, it is to be understood that when one component is referred to as being “connected or coupled directly” to another component, it may be connected to or coupled to the other component without another component intervening therebetween.

It will be further understood that terms “comprises/includes” or “have” used in the present specification specify the presence of stated features, numerals, steps, operations, components, parts, or a combination thereof, but do not preclude the presence or addition of one or more other features, numerals, steps, operations, components, parts, or a combination thereof.

FIG.1illustrates a battery system according to an embodiment.

Referring toFIG.1, the battery system1includes a battery10, a relay20, a current sensor30, and a battery management system (BMS)40.

The battery10includes a plurality of battery cells Cell1to Celln that are electrically connected. In some embodiments, the battery cells may be rechargeable batteries. A predetermined number of battery cells may be connected in series to constitute a battery module, and a predetermined number of battery modules may be connected in series and parallel to constitute the battery10to supply desired power. Each of the battery cells Cell1to Celln is electrically connected to the BMS40through wires.

InFIG.1, the battery10includes the plurality of battery cells Cell1to Celln connected in series, and is connected between two output terminals OUT1and OUT2of the battery system1. The relay20is connected between a positive electrode of the battery10and the output terminal OUT1, and the current sensor30is connected between a negative electrode of the battery10and the output terminal OUT2. The constituent elements illustrated inFIG.1and a connection relationship between the constituent elements are examples, and the present invention is not limited thereto.

The relay20controls electrical connection between the battery system1and an external device. When the relay20is turned on, the battery system1and the external device are electrically connected to perform charging or discharging, and when the relay20is turned off, the battery system1and the external device are electrically separated. In this case, the external device may serve as a charger in a charging mode in which the battery10is charged by supplying power, or a load in a discharge mode in which power stored in the battery10is discharged.

The current sensor30is connected in series to a current path between the battery10and the external device. The current sensor30may measure a current flowing through the battery10, i.e., a charging current and a discharging current, and may transmit a measurement result to the BMS40.

The BMS40may collect and analyze various information related to the battery cells Cell1to Celln to control charging and discharging of the battery cells, cell balancing, a protection operation, and the like, and may control an operation of the relay20. For example, the BMS40may control charging of the battery10in a normal mode (NORMAL MODE) or an eco-friendly mode (ECO MODE) depending on user selection.

In the normal mode (NORMAL MODE), the battery10uses a maximum usable battery capacity (hereinafter, a first battery capacity) within a designed range, and uses a charging method selected by a user among a slow charging method or a rapid charging method to charge the battery10. For example, the normal mode (NORMAL MODE) is a method of using and managing the battery10in an initially designed state.

In the eco-friendly mode (ECO MODE), the battery10uses a narrower battery capacity (hereinafter, second battery capacity) than the maximum usable battery capacity in a designed range, and charges the battery10by a slow charging method. For example, the eco-friendly mode (ECO MODE) is a battery management method for extending the cycle-life of the battery10, and may be set by user selection. That is, the eco-friendly mode (ECO MODE) is a battery management method that slows down an aging rate of the battery10by limiting excessive use of the battery capacity and the rapid charging method.

A state of charge (SOC) is an amount of energy that is currently stored in the battery10, and a unit thereof is percent (%). When the battery10is fully charged, the state of charge SOC is 100%. When the battery10is completely discharged, the state of charge (SOC) is 0%. When the fully charged battery10starts to be discharged, the state of charge (SOC) decreases to 100%, 80%, 60%, etc. as time elapses. In the meantime, the state of charge (SOC) cannot be directly measured, and the BMS40may estimate the state of charge (SOC) by an indirect method such as a conventionally known current integration method or a voltage measurement method. The BMS40may estimate the state of charge (SOC) in a predetermined period or in real time.

The battery capacity is a total amount of energy that the battery10can store, and the unit is ampere-hours (Ah) and represents how long a constant current can flow. For example, when a current of 1 A flows for 1 hour, the battery capacity is 1 AH, and when it flows for 2 hours, the battery capacity is 2 AH.

According to an embodiment, the first battery capacity may include a battery capacity having a range between a first lower limit SOC and a first upper limit SOC provided in a design and production process of the battery10. For example, the first battery capacity may include a battery capacity defined as 0% to 100%, or substantially in a range of 2% to 96% in consideration of a design margin, resistance, calculation error, and the like. The second battery capacity may include a battery capacity in a narrower region than the first battery capacity in order to slow the aging rate of the battery10. Specifically, the second battery capacity may include a battery capacity having a range between a second lower limit SOC that is a predetermined magnitude that is greater than the first lower limit SOC and a second upper limit SOC that is a predetermined magnitude that is smaller than the first upper limit SOC. For example, the second battery capacity may include a battery capacity defined as a range between 30% and 80%.

In the normal mode (NORMAL MODE), the BMS40enters a charging mode for supplying power to the battery10when the state of charge (SOC) reaches the first lower limit SOC (e.g., 2%). When a real-time state of charge (SOC) reaches the first upper limit SOC (e.g., 96%) by supplying power to battery10, the BMS40may end the charging mode. In addition, in the eco-friendly mode (ECO MODE), the BMS40enters a charging mode for supplying power to the battery10when the state of charge (SOC) reaches the second lower limit SOC (e.g., 30%). When a real-time state of charge (SOC) reaches the second upper limit SOC (e.g., 80%) by supplying power to battery10, the BMS40may end the charging mode.

Slow charging and rapid charging are battery charging methods that are divided depending on the charging speed. The slow charging is a slow charging method for completing the charging of the battery10after exceeding a predetermined reference time. The rapid charging is a fast charging method for completing the charging of the battery10within a predetermined reference time.

In the meantime, when using the battery at a maximum capacity, e.g., when the first lower limit SOC (e.g., 2%) and the first upper limit SOC (e.g., 96%) are repeatedly used, or when using an extended battery capacity (1% to 97% or 0% to 99%), aging of the battery10may be accelerated. In addition, when the battery10is charged by the rapid charging method, the aging of the battery10may be accelerated compared to when the battery10is charged by the slow charging method.

As the battery10ages with use after being manufactured, a total amount of storable energy (battery capacity) also decreases. A state of health (SOH) is a performance index that is obtained by comparing an ideal battery state with a current battery state. For example, although the battery10initially had a battery capacity of 1000 mAh, the battery capacity may decrease to 850 mAh after use for a predetermined period of time. Then, the battery state of health (SOH) becomes 85%.

For reference, when the battery state of health (SOH) is 100%, states of charge (SOC) at the time of full charge and full discharge of the battery10are 100% and 0%, respectively. In addition, when the battery state of health (SOH) is 85%, the states of charge (SOC) at the time of full charge and full discharge of the battery10are 100% and 0%, respectively. That is, the state of charge (SOC) is 100% when the energy that can be filled in the battery10is fully filled, and is 0% when the energy is exhausted, regardless of the state of health (SOH) of the battery. However, the battery10with a battery state of health (SOH) of 100% can supply a total of 1000 mAh of energy after being fully charged, whereas the battery10with a battery state of health (SOH) of 85% can only supply a total of 850 mAh energy after being fully charged.

That is, the battery capacity decreases in response to the battery state of health (SOH). For example, a time when the battery state of health (SOH) is decreased to a predetermined reference value, e.g., 80%, may be regarded as a battery replacement time. When the battery state of health (SOH) falls below 80%, the battery capacity is rapidly deteriorated and the battery10cannot perform its original role.

FIGS.2A and2Billustrate views for describing a normal mode according to an embodiment, andFIGS.3A and3Billustrate views for describing an eco-friendly mode according to an embodiment.

According to an embodiment, a first key Key_1 for executing the eco-friendly mode (ECO MODE) may be provided on a user interface. When a user selects (ON) or non-selects (OFF), the first key Key_1 that performs the eco-friendly mode (ECO MODE), the BMS40may control the charging of the battery10in the eco-friendly mode (ECO MODE) depending on user selection (ON) or the normal mode (NORMAL MODE) depending on non-selection (OFF). For example, the BMS40may receive a first key-on signal for selecting the first key Key_1 or a first key-off signal for not selecting the first key Key_1 from an electronic control unit (ECU).

According to another embodiment, the first key Key_1 for executing the eco-friendly mode (ECO MODE) and a second key Key_2 for executing the normal mode (NORMAL MODE), which can be manipulated by the user, may be provided in a user interface. When the user selects (ON) of the first key Key_1 for executing the eco-friendly mode (ECO MODE), the BMS40may control the charging of the battery10in the eco-friendly mode (ECO MODE). When the user selects (ON) of the second key Key_2 for executing the normal mode (NORMAL MODE), the BMS40may control the charging of the battery10in the normal mode (NORMAL MODE). For example, the BMS40may receive the first key-on signal for selecting the first key Key_1 or a second key-on signal for selecting the second key Key_2 of the normal mode (NORMAL MODE) from the electronic control unit (ECU).

Referring toFIG.2A, in an ON state of the normal mode (NORMAL MODE), the first battery capacity is set to a usable battery capacity (hereinafter, the available battery capacity), and rapid charging is enabled. Accordingly, the BMS40may control the charging of the battery10in a first battery capacity range by the fast charging or slow charging method depending on the user selection.

Referring toFIG.2B, when the battery10is used and managed in the normal mode (NORMAL MODE), an end of life (EOL) of the battery10may be determined as a time when the available battery capacity reaches a predetermined reference value (80%) compared to an initial state (100%). That is, when the battery state of health (SOH) reaches 80%, the battery10should be discarded. In this case, the end of life (EOL) may be determined depending on a number of charge and discharge cycles. For example, a lithium-ion battery is determined to have reached the end of life (EOL) when 300 to 500 charge and discharge cycles have elapsed.

Referring toFIG.3A, in the ON state of the eco-friendly mode (ECO MODE), the second battery capacity is set to an available battery capacity, and the fast charging method is disabled. Accordingly, the BMS40may control the charging of the battery10in a second battery capacity range by the slow charging method. In this case, the second battery capacity may be set to a battery capacity in a range that is smaller than the first battery capacity.

Referring toFIG.3B, when the battery10is used and managed in the eco-friendly mode (ECO MODE), an end of life (EOL+α) of the battery10may be extended for a predetermined period of time a than when the battery10is used and managed in the normal mode (NORMAL MODE).

FIG.4illustrates a flowchart describing a method of extending cycle-life of a battery by charging the battery in a normal mode or an eco-friendly mode depending on user selection according to an embodiment.

Hereinafter, a battery management method and a battery system providing the method will be described with reference toFIG.1toFIG.4.

Referring toFIG.4, the BMS40determines whether the eco-friendly mode (ECO MODE) is in an on state by user selection (S10).

According to an embodiment, a first key Key_1, for executing the eco-friendly mode (ECO MODE) may be provided on a user interface (not illustrated). When a user selects the first key Key_1, the BMS40may determine the eco-friendly mode (ECO MODE), while when the user does not select the first key Key_1, the BMS40may determine the normal mode (NORMAL MODE). That is, when the user does not take any action, the BMS40may determine the normal mode (NORMAL MODE). For example, the BMS40may receive a first key-on signal for indicating selection of the first key Key_1 or a first key-off signal for indicating non-selection of the first key Key_1 from an electronic control unit (ECU).

According to another embodiment, the first key Key_1 for executing the eco-friendly mode (ECO MODE) and a second key Key_2 for executing the normal mode (NORMAL MODE) may be provided in a user interface. When the user selects the first key Key_1, the BMS40may determine the eco-friendly mode (ECO MODE), while when the user does not select the second key Key_2, the BMS40may determine the normal mode (NORMAL MODE). For example, the BMS40may receive the first key-on signal for selecting the first key Key_1 or a second key-on signal for selecting the second key Key_2 of the normal mode (NORMAL MODE) from the electronic control unit (ECU).

Next, when the eco-friendly mode (ECO MODE) is in an off state (S10, No), the BMS40controls the charging of the battery10in the normal mode (NORMAL MODE) (S20).

In step S20, first, the BMS40diagnoses whether a current state of charge (SOC) reaches a first lower limit SOC of the first battery capacity (S21).

The normal mode (NORMAL MODE) is a method of managing the battery10as designed. The normal mode (NORMAL MODE) uses the first battery capacity, which is a maximum battery capacity that is usable in the designed range. In this case, the first battery capacity may be a battery capacity having a range between a first lower limit SOC and a first upper limit SOC provided in a design and production process of the battery10. Assuming an ideal state, the first battery capacity may include a battery capacity defined in a range between 0% and 100%. The BMS40may calculate the current state of charge (SOC) by estimating the state of charge (SOC) in a predetermined period or in real time.

In step S20, when the state of charge SOC reaches the first lower limit SOC (S21, Yes), the BMS40enters a charging mode for supplying power to the battery10(S22).

The BMS40may control the charging of the battery10in a first battery capacity range by the fast charging or slow charging method depending on the user selection. For example, when the user selects the rapid charging, the BMS40may control power to be supplied to the battery10through rapid charging.

According to an embodiment, when there is no user selection of the charging method, the BMS40may request the user to select the charging method through the electronic control unit (ECU). The electronic control unit (ECU) may control a message requesting selection of one of the fast charging and the slow charging method to be displayed on a user interface.

In step S20, the BMS40diagnoses whether a current state of charge (SOC) reaches a first upper limit SOC of the first battery capacity (S23).

In the charging mode, the battery10receives power from an external device, and the state of charge (SOC) increases as time elapses. For example, in the case where charging is started when the state of charge (SOC) is 0%, the state of charge (SOC) may gradually increase to 10%, 30%, or 50% as time elapses.

Next, when the eco-friendly mode (ECO MODE) is in an on state (S10, Yes), the BMS40controls the charging of the battery10in the eco-friendly mode (ECO MODE) (S30).

In step S30, first, the BMS40diagnoses whether the state of charge (SOC) reaches a second lower limit SOC of the second battery capacity (S31).

The eco-friendly mode (ECO MODE) is a battery management method for extending the cycle-life of the battery10, and may be set by user selection. In the eco-friendly mode (ECO MODE), the second battery capacity, which is a battery capacity in a narrower region than that of the first battery capacity, is used. In this case, the second battery capacity may include a battery capacity having a range between a second lower limit SOC that is a predetermined magnitude that is greater than the first lower limit SOC and a second upper limit SOC that is a predetermined magnitude that is smaller than the first upper limit SOC. For example, the second battery capacity may include a battery capacity defined as a range between 30% and 80%.

Referring toFIG.3A, the first lower limit SOC of the first battery capacity is smaller than the second lower limit SOC of the second battery capacity, and the first upper limit SOC is greater than the second upper limit SOC of the second battery capacity.

In step S30, when the state of charge SOC reaches the second lower limit SOC (S31, Yes), the BMS40enters a charging mode for supplying power to the battery10(S32).

Since the rapid charging method is disabled, the BMS40may control the charging of the battery10in the second battery capacity range by the slow charging method. When the state of charge (SOC) reaches the second lower limit SOC, e.g., 30%, the BMS40may control the battery10to be charged without further discharging.

In step S30, the BMS40diagnoses whether the state of charge (SOC) reaches the second upper limit SOC of the second battery capacity (S33).

Next, when the current state of charge (SOC) reaches the first upper limit SOC or the second upper limit SOC (S23, Yes), the BMS40may end the charging mode S40.

When the battery10is fully charged up to the first upper limit SOC, the BMS40may end charging of the battery10(S40). For example, the BMS40may end the charging of the battery10when the state of charge (SOC) reaches 100%.

When the battery10is fully charged up to the second upper limit SOC, the BMS40may end charging of the battery10(S40). For example, in the case where charging is started when the state of charge (SOC) is 30%, the state of charge (SOC) may gradually increase to 30% or 70% as time elapses. When the state of charge (SOC) reaches the second upper limit SOC, e.g., 80%, the BMS40may end the charging mode such that the battery10is no longer charged.