Abstract:
Electric apparatus, computer apparatus, controller, and battery switching method and program is provided to prevent a system shutdown caused by a reduction of electric power from a battery. A computer apparatus is constructed to be able to accept and be powered by a rechargeable main battery and a rechargeable sub-battery. An embedded controller in the computer apparatus monitors a remaining capacity at a pre-specified temperature of the sub-battery under discharge by receiving information from CPU. When the monitored temperature exceeds a predetermined temperature and when the monitored remaining capacity becomes less than a predetermined capacity, the embedded controller receives electric power from the main battery by switching the power supply circuit to provide power from the main battery instead of the sub-battery.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an electric apparatus such as a notebook PC (notebook personal computer) and in particular to an electric apparatus to which a charge-discharge battery can be connected.  
           [0002]    Secondary batteries, which can be repeatedly reused by recharging after they are discharged, are widely used in electric apparatuses such as notebook PCs, for example. Nickel-cadmium batteries (nicad batteries), lithium ion batteries, and the like are typically used as the secondary batteries. Also, lithium polymer batteries, which are safe and suitable for slim designs, will come into widespread use.  
           [0003]    An electric apparatus such as a notebook PC uses as its secondary battery a main battery which it included in it as standard equipment. In addition to this main battery, a “sub-battery”, which is an optional expansion battery, is used in some electric apparatuses. Conventionally, these electric apparatuses using a sub-battery besides the main battery discharges the sub-battery first, then, after remaining charge in the sub-battery becomes 0% (nearly 0%) of full charge, switches to the main battery and discharges the main battery until its remaining charge becomes 0% (nearly 0%).  
           [0004]    Typically, square lithium ion cells are used in a sub-battery, for example. The sub-battery using lithium ion cells has high internal resistance and contains a fuse and therefore a large discharge current may cause high self-heating. In recent years, the maximum power consumption in a notebook PC has increased. When a program that places system hardware such as its CPU in full operation is executed, a discharge may cause an excessive rise in temperature. In such a case, a protect function may be activated in order to protect the apparatus against the excessive temperature rise in the battery cells and as a result, the apparatus may shut down.  
           [0005]    [0005]FIG. 6 shows data on temperatures during discharging according to a background art. The horizontal axis indicates time and the vertical axis indicates temperatures. Shown in FIG. 6 are data on temperatures in a sub-battery protection FET, sub-battery cells, main battery protection FET, and main-battery cells, and ambient temperature.  
           [0006]    Assumption here is that the CPU is operating in normal mode and a current of 5,500 mA flows from the battery cells. The maximum power consumption of the CPU is high and the temperature of the sub-battery protection FET and sub-battery cells rises with time. It can be seen that at the first point of time in FIG. 6 the CPU enters low-speed mode because of an excessively large current, resulting in reduction in performance. As a result, the temperature of the sub-battery protection FET drops temporarily but then continues to rise. On the other hand, the temperature rise slope of the sub-battery cells becomes slightly gentle after the first point of time but continues to rise. At the second point of time at which the temperature exceeds 60Â° C. (at the point where it rises to 63Â° C., for example), a protect circuit within the battery may be activated to shut off power supply from the sub-battery to the system. Such unexpected shutoff of power supply from the sub-battery to the system is undesirable.  
           [0007]    The present invention has been made in order to solve the problem and a purpose of the present invention is to prevent shutoff of electric power supply from a battery to a system.  
           [0008]    Another purpose of the present invention is to prevent shutdown of a plurality of separate battery units and use them to the fullest.  
         BRIEF SUMMARY OF THE INVENTION  
         [0009]    To achieve these purposes, the present invention stops discharge of a first battery, which is a “sub-battery”, and starts discharge of a second battery, which is a main battery, when the temperature of cells of the sub-battery becomes high due to discharge of the sub-battery. That is, an electronic apparatus to which the present invention is applied comprises a first battery for supplying electric power to a main body by discharging after charging thereof; a second battery being comprised of another unit different from the first battery and supplying electric power to the main body; a controller for stopping supply of electric power by the first battery to switch to supply of electric power to said main body by said second battery when said electric power is supplied to said main body under the condition that a temperature of said first battery exceeds a predetermined temperature.  
           [0010]    The controller of the electric apparatus to which the present invention is applied presets a predetermined temperature just below a temperature at which a protect circuit such as a FET is activated. The controller monitors the temperature of the cells in the first battery in discharge. If the monitored temperature of the cells exceeds the predetermined temperature, the controller switches to an attached second battery before the protect circuit is activated to shut down the system (main body). The controller can stop power supply from the first battery and causes the second battery to supply to the main body when the remaining capacity of the first battery decreases below a predetermined value.  
           [0011]    The electric apparatus to which the present invention is applied comprises means for monitoring the temperature of a battery supplying electric power to a main body to which it is connected; means for monitoring the remaining capacity of the battery; means for making switchover to electric power supply from a different electric power source different from the battery connected to the main body if the temperature of the battery monitored by the temperature monitor means exceeds a predetermined temperature and the remaining capacity monitored by the remaining capacity monitor means decreases below a predetermined capacity; and means for presenting an alarm message to a user if no electric power sources can discharge.  
           [0012]    The switching means can switch to power supplied by the battery if another battery, which is the different power source mentioned above, becomes exhausted after supplying electric power by the different battery to said main body. The term “exhausted” refers to not only a state in which the battery is fully exhausted but also to a state in which a small amount of capacity remains but the battery is practically “exhausted”, or nearly exhausted, and cannot function to supply power to the main body.  
           [0013]    According to the present invention, a power supply (such as an AC adapter) connected to a commercial electric power source may be contemplated as another power source. If for some reason power is supplied from a battery to the main body under the condition that a power supply such as an AC adapter is connected to the main body, discharge from the battery is stopped and switchover to discharge from the power supply such as the AC adapter is made based on a rise in temperature of the battery, for example.  
           [0014]    According to the present invention, there is provided a computer apparatus arranged such that a rechargeable or charge-discharge main battery and a rechargeable or charge-discharge sub-battery can be connected to it, comprising temperature monitor means for monitoring the temperature of a sub-battery that is discharging; remaining capacity monitor means for monitoring the remaining capacity of the sub-battery; and battery switching means for switching from the sub-battery to the main battery for receiving electric power supply from the main battery if the temperature monitored by the temperature monitor means exceeds a predetermined temperature and the remaining capacity monitored by the remaining capacity monitor means decreases below a predetermined capacity. The predetermined temperature may be 60Â° C. for example if only the temperature condition is monitored, or the temperature may be 55Â° C. for example and the predetermined capacity may be 20% if the remaining capacity is also monitored.  
           [0015]    The computer may further comprise determination means for determining whether the remaining capacity of the main battery is substantially exhausted after the computer receives power supply from the main battery through switching by the battery switching means. The battery switching means makes switchover to the sub-battery for receiving power supply from the sub-battery if the determination means determines that the remaining capacity of the main battery is substantially exhausted.  
           [0016]    From another point of view, the computer according to the present invention comprises first connection means capable of connecting a first battery unit; second connection means capable of connecting a second battery unit different from the first battery unit; discharge transferring means for transferring to discharge from the second battery unit by using the second connection means before a protection facility of the first battery unit is activated to stop power supply to the system; and execution means for executing a predetermined suspend process if the first and second battery units are no longer dischargeable.  
           [0017]    The discharge transferring means detects the temperature and remaining capacity of a battery cell in the first battery unit and, if predetermined conditions are met, transfers to discharge from the second battery cell. The predetermined conditions may be that the detected temperature of the battery cell is 55Â° C. or higher and the remaining capacity is 20% or less, for example. The effective conditions under which a protection circuit is activated may be that the temperature of the battery cell is  63 Â° C. and the remaining capacity is 13%, for example.  
           [0018]    A controller according to the present invention comprises monitor means for monitoring the temperature and remaining capacity of a battery cell in a first battery unit connected to a system main body for discharging to the system main body; and switching means for making switchover to discharge from a second battery unit connected to the system main body if the temperature monitored by the monitor means exceeds a predetermined value and the remaining capacity decreases below a predetermined value.  
           [0019]    According to the present invention, there is provided a battery switching method for switching between a plurality of battery units connected to a main body to supply electric power to the main body, comprising the steps of: detecting the cell temperature of the battery unit that is discharging; comparing the detected cell temperature with a temperature predetermined based on the operating temperature of a battery protection facility; and making switchover to discharge from another battery unit based on the result of the comparison. The method may further comprise the steps of: detecting the remaining capacity of the battery unit that is discharging; and making switchover to discharge from the another battery unit if the detected capacity is less than a predetermined capacity predetermined based on the battery protection facility. The method may further comprises the step of executing a predetermine suspend process if the temperatures of all of the plurality of battery units exceed the predetermined temperature and the remaining capacities of all of the plurality of battery units are less than the predetermined capacity.  
           [0020]    Furthermore, the present invention may be characterized by a battery switching method for switching between electric power supply from a commercial power source to which a main body is connected and a battery unit to which the main body is connected to supply of electric power to the main body, comprising the steps of: supplying electric power to the main body by discharge from the battery unit to which the main body is connected under the condition that the power supply is connected to the main body; and stopping discharge from the battery unit and making switchover to discharge from the power supply if the cell temperature of the battery unit that is discharging exceeds a predetermined temperature.  
           [0021]    The present invention can be contemplated as a program executed by a computer.  
           [0022]    The present invention is characterized by a program for causing a computer to which a plurality of battery units can be connected to implement the functions of: detecting the cell temperature of one of the plurality of battery units that is discharging; presetting a reference temperature determined based on a condition under which battery protection is activated and storing the reference temperature in a memory; comparing the detected cell temperature with the stored reference temperature; and making switchover to discharge from another battery unit connected if the cell temperature exceeds the reference temperature. The program further causing the computer to implement the functions of: detecting the remaining capacity of the battery unit that is discharging; presetting a reference capacity determined based on a condition under which battery protection is activated and storing the reference capacity in the memory; comparing the detected remaining capacity with the stored reference capacity; and making switchover to discharge from another battery unit connected if the remaining capacity is less than the reference capacity.  
           [0023]    The program to be executed by a computer may be provided as a recording medium on which it is stored in a computer readable form. The storage medium may be a floppy disk or a CD-ROM, for example. The program may be read by a floppy disk drive or a CD-ROM reader, stored in a memory such as a flash ROM, and executed by the computer.  
           [0024]    Alternatively, the program may be provided by a program transmission device to a notebook computer over a network, for example. The program transmission device may be provided in a server at a host site and may include a memory for storing the program and program transmission means for providing the program over the network. Furthermore, the program may be preinstalled in a computer and provided to a user when the computer is provided to the user. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0025]    Some of the purposes of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:  
         [0026]    [0026]FIG. 1 shows a hardware configuration of a computer system, which is an electric apparatus to which the present embodiment is applied;  
         [0027]    [0027]FIG. 2 shows a power supply circuit to which the present embodiment is applied;  
         [0028]    [0028]FIG. 3 show a flowchart of a process of a power supply method to which the present embodiment is applied;  
         [0029]    [0029]FIG. 4 shows temperature data during discharge in a case where the power supply method according to the present embodiment is used;  
         [0030]    [0030]FIG. 5 shows a configuration for implementing an interface with a user; and  
         [0031]    [0031]FIG. 6 shows temperature data during discharge according to the background art. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the present invention is shown, it is to be understood at the outset of the description which follows that persons of skill in the appropriate arts may modify the invention here described while still achieving the favorable results of this invention. Accordingly, the description which follows is to be understood as being a broad, teaching disclosure directed to persons of skill in the appropriate arts, and not as limiting upon the present invention.  
         [0033]    Referring now more particularly to the accompanying drawings, FIG. 1 shows a hardware configuration of a computer system  10 , which is an electric apparatus to which the present embodiment is applied. A computer apparatus including this computer system  10  (hereinafter sometimes simply referred to as the “system”) may be a notebook personal computer (notebook PC) that is compliant with OADG (Open Architecture Developer&#39;s Group) specifications and includes a given operating system (OS).  
         [0034]    A CPU  11  in the computer system  10  shown in FIG. 1 functions as the brain of the entire computer system  10  and executes programs, including a utility program, under the control of the OS. The CPU  11  is interconnected with components of the computer system  10  through three busses: a FSB (Front Side Bus)  12 , which is a system bus, a PCI (Peripheral Component Interconnect) bus  20 , which is a fast I/O device bus, and an LPC (Low Pin Count) bus  40 , which is an I/O device bus. The CPU  11  stores program codes and data in a cache memory to facilitate fast processing. In recent years, a CPU  11  incorporates 128K bytes or so of SRAM memory as a primary cache. In order to make up for a shortage of memory capacity, 512K to about 2M of secondary cache  14  is provided through a BSB (Back Side Bus)  13 , which is a dedicated bus. The BSB  13  may be omitted and the secondary cache  14  may be connected onto the FSB  12 , thereby avoiding an increase in the number of terminals in the package to reduce costs.  
         [0035]    The mode of the CPU  11  used in the present embodiment can be controlled. For example, the CPU  11  can operate in normal mode and low-speed mode (low power mode). To lower the operating speed of the CPU  11 , SpeedStep technology (which lowers the operating frequency and voltage of a processor) from Intel in the U.S.A. or throttling technology (which periodically turns on/off a processor to in effect reduce operating frequency), for example, may be used. By causing the CPU  11  to operate in low power mode, the clock frequency of the CPU  11  can be reduced from a normal frequency of 850 MHz to 750 MHz and the voltage of the CPU  11  can be decreased from a normal voltage of 1.6 V to 1.35 V, for example.  
         [0036]    The FSB  12  and the PCI bus  20  are connected with each other via a CPU bridge (host-PC bridge)  15  called a memory/PCI chip. The CPU bridge  15  includes a memory controller function for controlling access to the main memory  16  and a data buffer for accommodating the difference in data transfer rate between the FSB bus  12  and the PCI bus  20 . The main memory  16  is writeable memory which is used as an area in which programs to be executed by the CPU  11  are loaded or a working area into which data is to be processed by the execution programs. The main memory  16  may be composed of a number of DRAM chips, for example, originally it may have 64 MB of memory capacity, and be expandable to 320 MB of memory. The execution programs includes an OS, drivers for operating hardware peripherals, application programs designed for specific tasks, and firmware such as BIOS (Basic Input/Output System) stored in a flash ROM  44 , which will be described later.  
         [0037]    A video subsystem  17  is a subsystem for implementing functions concerning video and includes a video controller. The video controller processes image instructions from the CPU  11  and writes image information resulting from the processed instructions into video memory. It reads the image information from the video memory and outputs it as image data on a liquid crystal display (LCD)  18 .  
         [0038]    The PCI bus  20  is capable of transferring data at a relatively fast speed. The PCI bus  20  is a standardized bus conforming to specifications of a width of 32 or 64 bits, a maximum operating frequency of 33 MHz or 66 MHz, and a maximum data transfer rate of 132 MB/second or 528 MB/second. Connected onto the PCI bus  20  are, an I/O bridge  21 , a Card Bus controller  22 , an audio subsystem  25 , a docking station interface (Dock I/F)  26 , and mini PCI connector  27 .  
         [0039]    The Card Bus controller  22  is a dedicated controller for directly coupling a bus signal on the PCI bus  20  to the interface connector (Card Bus) of a Card Bus slot  23 . A PC Card  24  can be connected to the Card Bus slot  23 . The docking station interface  26  is hardware to which a docking station (not shown), which is a functionality expansion device for the computer system  10 , is to be attached. When the notebook PC is set in the docking station, hardware components connected onto an internal bus in the docking station are connected to the PCI bus  20  through the docking station interface  26 . A mini PCI card  28  is connected to the mini PCI connector  27 .  
         [0040]    The I/O bridge  21  has a bridge function between the PCI bus  20  and the LPC bus  40 . It also has a DMA controller function, programmable interrupt control (PIC) function, programmable interval timer (PIT) function, IDE (Integrated Device Electronics) interface function, USB (Universal Serial Bus) function, and SMB (System Management Bus) interface function and contains a real time clock (RTC).  
         [0041]    The DMA controller function is the function of providing data transfer between a peripheral device such as FDD and the main memory  16  without the intervention of the CPU  11 . The PIC function is the function of causing a predetermined program (interrupt handler) to be executed in response to an interrupt request (IRQ) from a peripheral device. The PIT function is the function of generating a timer signal at predetermined intervals. The IDE interface function implements an interface to which an IDE hard disk drive (HDD)  31  is connected and also a CD-ROM drive  32  is connected using ATAPI (AT Attachment Packet Interface). IDE devices of other types such as a DVD (Digital Versatile Disc) drive may be connected instead of the CD-ROM drive  32 . The external storage devices such as the HDD  31  and CD-ROM drive  32  are installed in an area called a “media bay” or “device bay” in the main body of the notebook PC. In some cases, the external storage devices included as standard equipment may be attached interchangeably and mutually exclusively with another device such as an FDD or battery pack.  
         [0042]    A USB port is provided in the I/O bridge  21 . The USB port is connected with a USB connector  30  provided for example in a wall of the main body of the notebook PC. Also connected to the I/O bridge  21  is an EEPROM  33  through the SM bus. The EEPROM  33  is memory for holding information such as a password or supervisor password registered by a user and the serial number of the product. The EEPROM  33  is nonvolatile and can be electrically everwritten. A plurality of connectors  47  are connected to the I/O bridge  21  through an AC 97 (Audio CODEC &#39;97) supporting modem functionality, an LCI (LAN Connect Interface) containing in a core chip for interfacing to Ethernet, a USB, and the like. A communication card can  48  be connected to each of the plurality of connectors  47 .  
         [0043]    The I/O bridge  21  connected also to a power supply circuit  50 . The power supply circuit  50  includes an AC adapter  51  to be connected to an AC 100 or 115 V commercial power source for performing AC/DC conversion, a secondary battery  52 , which is repeatedly charged and discharged and may be a nickel metal hydride battery or nickel cadmium battery, lithium ion battery, or lithium polymer battery, a battery switching circuit  54  for switching between the AC power from the AC adapter  51  and battery power from the secondary battery  52 , a DC/DC converter for generating a direct current constant voltage of +15 V, +5 V, +3.3 V or so used in the computer system  10 , and other circuits. The secondary battery  52  is an intelligent battery containing a CPU and communicating with an embedded controller  41  (which will be described later) according to the SBS (Smart Battery System) specifications, for example.  
         [0044]    Provided in the core that forms the I/O bridge  21  are an internal register for managing power in the computer system  10  and a logic (state machine) for power management in the computer system  10 , including control of the internal register. The logic sends and receives signals to and from the power supply circuit  50  to recognize the actual status of power supply from the power supply circuit  50  to the computer system  10 . The power supply circuit  50  controls power supply to the computer system according to directions from this logic.  
         [0045]    The LPC bus  40  is an interface standard designed for connecting a legacy device to a system having no ISA bus. It communicates commands, addresses, and data the same four signal lines (LAD signals) at an operating clock of 33 MHZ (for example, 8-bit data is transferred by 4 bits, 2 clocks). Connected on the LPC bus  40  are the embedded controller  41 , a gate array logic  42 , a flash ROM  44 , and a Super I/O controller  45 . The LPC bus  40  is also used for connecting peripherals such as a keyboard and mouse controller that operate at relatively low speeds. An I/O port  46  is connected to the Super I/O controller  45  for controlling the drive of an FDD, input and output of parallel data (PIO) through a parallel port, and input and output of serial data (SIO) through a serial port.  
         [0046]    The embedded controller  41  controls a keyboard, not shown, and is connected to the power supply circuit  50  to provide part of power management functionality using a power management controller (PMC) contained in the embedded controller  41  in combination with the gate array logic  42 .  
         [0047]    [0047]FIG. 2 shows a power supply circuit to which the present embodiment is applied. The secondary battery  52  side and system side of the circuit are shown in FIG. 2. Provided on the secondary battery  52  side are a main battery  60 , which is a first battery unit, and a sub-battery  61 , which is a second battery unit. Some notebook PCs may be originally equipped with a battery pack as the main battery  60  and provided with a sub-battery  61  as an optional expansion battery. If the main battery  60  and sub-battery  61  are connected with each other in a notebook PC, typically (discharge from) the sub-battery  61  is used first and, when the remaining capacity of the sub-battery  61  becomes nearly zero (exhausted), the main battery  60  is used. This is because if the main battery  60  were discharged first (for example, if the sub-battery  61  is removed and another device (for example a CD-ROM) is attached after the main battery  60  is consumed), a problem such as a shortage of battery would occur.  
         [0048]    As shown in FIG. 2, the sub-battery  61 , which is an intelligent battery, comprises battery cells  62 , which may be lithium ion cells, a current measurement circuit  63  for measuring the value of a current charged into and discharged from the battery cells  62 , a voltage measurement circuit for detecting the voltage of the battery cells  64 , a CPU  66 , which is a microcomputer for controlling the second cell  61 , a first FET (Field Effect Transistor)  71 , which is a discharge stopping transistor for protecting the sub-battery  61  against abnormal discharge, and a second FET  72 , which is a charge stopping transistor for protecting the sub-battery  61  against abnormal charging. Fuses are provided within the battery cells  62  for protecting the system against an abnormal current flow. These fuses are protect elements of a type that melts to shutoff power if an overcurrent flows. These fuses cannot recovers once they have operated (melted). The CPU  66  receives the result of the detection from a current measurement circuit  63  and voltage measurement circuit  64  to know the capacity of the battery cell  62 . The CPU  66  uses a temperature sensor (not shown) provided in the vicinity of the battery cells  62  to know the temperature of the battery cell  62 . The obtained information is provided to the embedded controller  41  in a data format compliant to SBS, for example. A configuration similar to that of the sub-battery  61  shown in FIG. 2 is provided for the main battery  60 . Instead of the FET, a PTC (Positive Temperature Coefficient) thermistor having resistance that drastically changes as its temperature exceeds a certain temperature may be used as a protective element.  
         [0049]    The system side shown in FIG. 2 includes a third and fourth FETs  73  and  74  which are controlled by the embedded controller  41  to switch between charge and discharge of the sub-battery  61 . It also includes a fifth and sixth FETs  75  and  76  which are controlled by the embedded controller  41  to switch between charge and discharge of the main battery  60 . When discharging the sub-battery  61 , the embedded controller  41  turns on the third and fourth FETs  73  and  74  and turns off the fifth and sixth FETs  75  and  76 . The embedded controller  41  outputs Low through its OUT 3  and OUT 4  terminals and Hi-Z (OPEN) through its OUTS and OUT  6  terminals.  
         [0050]    Taking the sub-battery  61  as an example, the first and second FETs  71  and  72  in the sub-battery  61  are normally set at on by the CPU  66 . When the temperature of the battery cells  62  increases, the CPU  66  turns off the first FET  71  in order prevent damage to the battery cells  62  due to blowout of fuses within the battery cells  62 . For example, if the temperature of the battery cells  62  increases to 63Â° C., its discharge current becomes 4,700 mA, and its remaining capacity decreases to 13%, the CPU  66  activates the protection circuit of the battery. As a result, the power supply from the sub-battery  61  to the system side is shut off, resulting in shutdown of the system. The present embodiment addresses the problem by improving the power supply method so that the sub-battery  61  and main battery  60  are fully consumed.  
         [0051]    [0051]FIG. 3 shows a flowchart of a power supply process according to the present embodiment. In this process, when the temperature of the sub-battery  61  does not become high and the battery capacity (remaining capacity) is not low, the sub-battery  61  is first discharged, then the main battery  60  is discharged, and finally a shutdown operation (activation of a battery exhaustion alarm) is performed. First, the embedded controller  41  outputs Low through OUT 3  and OUT 4  terminals and Hi-Z (OPEN) through OUT 5  and OUT  6  terminals and turns on the third and fourth FETs  73  and  74  and off the fifth and sixth FETs  75  and  76  to start discharging from the sub-battery  61  (step  101 ). Then, it determines based on information obtained from the CPU  66  of the sub-battery  61  whether the temperature of the sub-battery  61  is as high as over 55Â° C. and the remaining capacity is as low as 20% or less (step  102 ). If so, the embedded controller  41  switches from the sub-battery  61  to the main battery  60 , and proceeds to step  108 . On the other hand, if the conditions at step  102  are not met, it determines that discharge from the sub-battery  61  can be continued and proceeds to step  103  and the subsequent steps.  
         [0052]    Determination at step  102  is based on not only a temperature rise but also the remaining capacity of the battery. The fuse provided in the battery cells  62  typically blows depending on the relationship between the temperature and the current value of the battery. Therefore, ideally the discharge current value as well as the temperature should be observed and the switching between the batteries should be performed based on these values. However, typically increases and decreases in the current value are frequently repeated and therefore it is difficult to determine an accurate discharge current. On the other hand, as the remaining capacity of the battery decreases, the voltage decreases and the current value increases accordingly. Therefore, simply the remaining capacity is observed instead of the current value and, depending on the temperature of the discharging battery and the observed remaining capacity, a changeover from the discharging battery to the other is made, according to the present embodiment. The predetermined temperature, 55Â° C., and the capacity, 20% at step  102  are determined based on a cell temperature of 63Â° C., a discharge current of 4,700 mA, and a remaining capacity of 13%, at which the protection function of the battery is activated to stop discharge to the system. If only the temperature condition is observed, it is determined whether the temperature of the battery exceeds 60Â° C.  
         [0053]    If the conditions at step  102  are not met, it is determined whether or not the sub-battery  61  becomes empty (nearly empty) (step  103 ). If it is not exhausted, the process returns to the determination at step  102 . On the other hand, if it is exhausted, it is determined whether or not the main battery  60  is available (step  104 ). If it is not available, the battery exhaustion alarm is activated (step  107 ), then the process ends. If the main battery  60  is available, the embedded controller  41  outputs Hi-Z (Open) through the OUT 3  and OUT 4  and LOW through the OUT 5  and OUT 6  terminals and turns off the third and fourth FETs  73  and  74  and on the fifth and sixth FETs  75  and  76  to switch to the main battery  60  (step  105 ). Then, it continues discharge from the main battery  60  until it becomes empty (nearly empty) (step  106 ), then the process ends through step  107 .  
         [0054]    On the other hand, if the conditions at step  102  are met, it is determined whether or not the main battery  60  is available (step  108 ). If it is not available, the process ends through step  107 . If the main battery  60  is available, changeover to the main battery  60  is made (step  109 ) and discharge from the main battery  60  is continued until it becomes empty (nearly empty) (step  110 ). After the main battery  60  becomes empty (nearly empty), changeover to the sub-battery  61  is made (step  111 ), then it is determined whether or not the same temperature and battery capacity (remaining capacity) conditions as in step  102  are restored (step  112 ). If the conditions at step  112  are met, the process ends through step  107 . On the other hand, if the temperature and remaining capacity conditions are restored, it is determined whether or not the sub-battery  61  is empty (nearly empty) (step  113 ). If it is not empty (not nearly empty), then the sub-battery  61  is discharged to the extent where the conditions at step  112  are not met. When it becomes empty (nearly empty), then the process ends through step  107 .  
         [0055]    While the determination is made based on the remaining capacity as well as the temperature in the process in FIG. 3, the battery unit switching may be made simply based on the temperature condition alone. For example, if the temperature of the sub-battery  61  becomes high (for example over 60Â° C., or 62Â° C. or  65 Â° C. depending on the types of the batteries), changeover to the operation on the main battery  60  is made. If the temperature of the secondary battery  61  decreased below 60Â° C., for example, after the main battery  60  is discharged, then the remaining capacity of the sub-battery  61  is discharged and eventually shutoff operation is performed.  
         [0056]    [0056]FIG. 4 shows temperature data during discharging by using the power supply method according to the present embodiment. The horizontal axis indicates time and the vertical axis indicates temperature. Shown in FIG. 4 are data on the temperature of first FET  71 , which is the protection FET of the sub-battery  61 , data on the temperature of the battery cells  62  of the sub-battery  61 , data on the temperature of the protection FET of the main battery  60 , data on the temperature of the battery cells of the main battery  60 , and the ambient temperature.  
         [0057]    The CPU  11  in the computer system  10 , which receives discharge from the sub-battery  61 , first operates in normal mode, and a current of approximately 5,500 mA is supplied to the CPU  11 . At the first point of time, the computer system  10  reduces the performance of the CPU  11  to switch to low power mode in which the current value is reduced to approximately 4,700 mA. As a result, the temperature of the first FET  71  temporarily decreases and, after a period of time, rises. On the other hand, the temperature of the battery cells  62  of the sub-battery  61  continues to increase. The temperature would continue to rise until the protection FET shuts down according to the background art as shown in FIG. 6. In the power supply method according to the present embodiment by contrast, the temperature of the battery cells  62  of the sub-battery  61  is monitored and, when it reaches 60Â° C., for example, (at the second point of time in FIG. 4), the embedded controller  41  on the system side stops the discharge from the sub-battery  61  and switches to discharge from the main battery  60 . The remaining capacity of the sub-battery  61  at this time point is reduced to 20% from 100%.  
         [0058]    As a result of the switch to the discharge from the main battery  60  at the second point of time, the temperature of the first FET  71  of the sub-battery  61  rapidly decreases and the temperature of the battery cells  62  also decreases. Then, when the remaining capacity of the main battery  60  decreases from 100% to nearly 0% (at the third point of time), the embedded controller  41  switches from the discharge from the main battery  60  to discharge from the sub-battery  61 . The switching at the third point of time is performed based on the precondition that the temperature of the battery cells  62  of the sub-battery  61  is lower than 60Â° C. In this way, this power supply method can prevent shutdown of the system while allowing the sub-battery  61  and main battery  60  to be fully consumed.  
         [0059]    [0059]FIG. 5 shows a configuration for implementing an interface with a user. The embedded controller  41  includes a memory  81  for storing commands to be set. The system includes a system BIOS (Basic Input/Output system)  82 , which is a basic input/output system for controlling the embedded controller  41 , an operating system (OS)  83  for providing the system management of the system  10  and a basic user operating environment, and a-utility program  84  for presenting messages to the user, all these components enabling an interface with the user.  
         [0060]    An operation in a case where no dischargeable batteries are available will be described below.  
         [0061]    An operation for providing an alarm will be described first. When the embedded controller  41  recognizes that the remaining battery capacity decreases to 20%, for example, it sets  0 x′ 4 E′ in the memory  81  to cause an SMI (System Management Interrupt). The system BIOS  82  reads the value set by the embedded controller  41  in the memory  81 . When the system BIOS  82  reads preset  0 x′ 4 E′, it generates an alarm sound and the utility program  84  displays an alarm message. For example, the alarm message displayed may be “The system will enter suspend mode due to overheating.” 
         [0062]    An operation for stopping discharge will be described. When the embedded controller  41  recognizes that the remaining capacity decreases to 19% or less, it sets  0 x′ 4 F′ in the memory  81  to cause an SMI. The system BIOS  82  reads the value set by the embedded controller  41  in the memory  81 . When the system BIOS  82  reads the set  0 x′ 4 F′, it performs an operation (suspend/hibernation) set by the user.  
         [0063]    In this way, the temperature of the cells of a discharging battery is detected, or both of the temperature of the cells and the remaining capacity of the battery unit are detected, and if the temperature of the discharging cells exceeds 60Â° C., for example, or the cell temperature exceeds 55Â° C. and the remaining capacity decreases to less than 20%, switchover from the discharge from the battery that meets these conditions to discharge from another attached battery unit is accomplished according to the present embodiment. If all the battery units meet these conditions, or the battery units become empty and no battery units are available for discharging, an operation set by the user is performed. These arrangements prevent sudden shutdown of the system and allow a plurality of battery units to be fully consumed.  
         [0064]    While the present embodiment has been described with respect to an example in which the two batteries, the main battery  60  and sub-battery  61 , are used, a detection and switching process similar to the process described above can be applied to three or more batteries. The plurality of batteries are not limited to those batteries contained in separate housings. The present invention can be applied to a case where one battery is divided into a plurality of units and used. While the notebook PC has been used as an example of the electric apparatus in the present embodiment, the method of the embodiment may be applied to other electric apparatus  
         [0065]    While the embodiment has been described in which the two batteries, the main battery  60  and sub-battery  61 , are used, the present invention can be applied to a case in which one secondary battery  52  is used and at the same time an AC adapter  51  is connected to the system. For example, a system may be controlled to receive power supplied from the secondary battery  52  even when the AC adapter  51  is connected, in order to reduce peak power during periods of extremely high electricity demand. In such a case, if the second battery  52 , which is the only secondary battery that can discharge, becomes unable to discharge due to a rise in its temperature, power can be supplied from discharge from the AC adapter  51  to prevent sudden shutdown of power supply.  
         [0066]    In the drawings and specifications there has been set forth a preferred embodiment of the invention and, although specific terms are used, the description thus given uses terminology in a generic and descriptive sense only and not for purposes of limitation.