JP3947881B2 - Portable information processing terminal and battery remaining amount display method - Google Patents

Description

  The present invention relates to a portable information processing terminal represented by a handy terminal, and more particularly to a portable information processing terminal including a replaceable battery pack and a method for displaying the remaining battery level.

Handy terminals are used for data collection and article management (inventory management, inventory, receipt / shipment processing, etc.). The handy terminal includes a rechargeable battery (also referred to as a battery pack) that can be replaced as a power source. When the remaining battery level is low, it is necessary to charge or replace the battery. If the battery is completely discharged while using the handy terminal, the power may be turned off and the data entered until then may be lost. For this reason, the battery remaining amount is displayed on the handy terminal (see Patent Document 1). The user can roughly determine the battery replacement time using the displayed remaining battery level as a guide.
JP-A-2004-157808 (paragraph 57)

  If the battery is charged during the operation at the handy terminal, the operation cannot be performed during that time, so that the work efficiency becomes very poor. For this reason, when the operation by the handy terminal takes a long time, the operation is usually continuously performed by replacing the battery. In this case, since the replacement of the battery is also temporarily interrupted, it is desirable to use the battery until the remaining amount is almost reached and to avoid the battery replacement as much as possible. In particular, if you are going to use a handy terminal in an outside business operation, prepare spare batteries, but because there are a limited number of spare batteries to carry, you want to use the batteries to the limit. There is a high demand. In order to satisfy such a requirement, it is necessary to accurately grasp the remaining battery level.

  However, since the display of the remaining battery level of the handy terminal so far is simply obtained by gradually obtaining the battery level from the battery voltage, as is often seen on mobile phones, the battery level is displayed accurately. It is difficult to grasp. For example, although there are battery level gauges that are displayed in three levels, the remaining level represented by each level is not uniform and inaccurate, so it is difficult to accurately grasp the remaining battery level.

  As what can display an accurate battery remaining amount, there is a battery remaining amount display as seen in a notebook personal computer (PC). In the notebook PC, a battery pack having a function of managing the remaining battery level is used, and the PC main body determines the remaining battery level based on information on the remaining battery level stored in the installed battery pack. Display in% units. However, since a battery pack having a function of managing the remaining battery capacity is very large and expensive, the use of such a battery pack in a handy terminal increases the size and cost of the device.

  If the handy terminal main body has a function for managing the remaining battery level as provided in the above battery pack, the remaining battery level can be accurately measured with a small and inexpensive general-purpose battery pack. It is possible to display. However, in this case, since the remaining battery level is estimated based on the fully charged state, when the battery pack is replaced, it becomes impossible to grasp the remaining battery level of the battery pack.

  An object of the present invention is to solve the above problems, use a small and inexpensive general-purpose battery pack, and accurately display the remaining battery level of the battery pack. To provide a display method.

In order to achieve the above object, the portable information processing terminal of the present invention is housed in the housing part when a display unit, a housing part in which a replaceable battery pack is housed, and power is supplied from the outside. Charging the battery pack, detecting whether the battery pack is fully charged, a battery replacement detecting unit detecting whether the battery pack stored in the storage unit has been replaced, and at least A measurement integration unit that measures the battery voltage and discharge current of the battery pack at regular time intervals and integrates the measured discharge current; and a pre-set current capacity at the time of full charge in the storage unit as a reference And a control means for estimating the remaining battery capacity of the stored battery pack and displaying it on the display section, and the control means allows the battery replacement detection section to detect the full charge after the charging section is detected. Battery exchange There until it is detected, the battery level is also displayed in the first display format I estimates based on the integrated value of the measured discharge current in the current capacity and the measurement integration unit, the After the battery replacement is detected by the battery replacement detection unit, the battery measured by the measurement integration unit with reference to the characteristic data representing the relationship between the battery voltage and the discharge amount at each of a plurality of different current values determine the amount of discharge from the voltage and discharge current, be displayed in a different second display format to the first display format I also estimate the remaining battery capacity on the basis of said current capacity and the discharge amount determined the It is characterized by.

The battery remaining amount display method of the present invention is a method for displaying the remaining battery amount of the battery pack, which is performed in a portable information processing terminal including a replaceable battery pack, and is a first method for charging the battery pack. A second step of detecting whether or not the battery pack is fully charged by the charging, a third step of detecting whether or not the battery pack has been replaced, and at least a battery of the battery pack A fourth step of measuring the voltage and the discharge current at regular time intervals and integrating the measured discharge current; and after the full charge is detected in the second step, the battery in the third step. until exchange is detected, the I also estimate the remaining battery capacity based on the integrated value of the resulting discharge current in the fourth step the current capacity of the full charge set in advance 1 A fifth step of displaying the display format, wherein after the battery replacement is detected in the third step, with reference to the characteristic data representing a relationship between the battery voltage and the discharge amount of each of a plurality of different current values the fourth step obtains a discharge amount from the measured battery voltage and discharge current of, the first display format I also estimate the remaining battery capacity on the basis of said current capacity and the discharge amount determined the And a sixth step of displaying in a different second display format .

In the present invention as described above, for a fully charged battery pack, the remaining battery capacity is estimated from the current capacity at full charge and the integrated value (discharge amount) of the discharge current measured by the measurement integration unit . . In this case, it is possible to display the remaining battery level in units of 1% with the fully charged state being 100%, so that the remaining battery level can be accurately grasped.

On the other hand, for the replaced battery pack, with reference to characteristic data (specifically, a two-dimensional map), a discharge amount is obtained from the battery voltage and discharge current measured by the measurement integration unit , and the obtained discharge is obtained. The remaining battery capacity is estimated from the amount and current capacity at full charge. In this case, it is possible to accurately estimate the remaining battery level, for example, in units of 25%, assuming that the state at full charge is 100%. It is possible to equalize the remaining amount represented. Therefore, it is possible to accurately grasp the remaining battery level.

  According to the present invention, the battery remaining amount can be accurately grasped, so that the battery can be used to the limit, and work efficiency can be improved.

  Further, according to the present invention, it is not necessary to use an expensive and large battery pack used in a notebook PC as the battery pack, and a small and inexpensive general-purpose battery pack can be used. This is also advantageous in terms of cost reduction and cost reduction.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration of a main part of a handy terminal which is an embodiment of the portable information processing terminal of the present invention, and FIG.

  Referring to FIG. 2, the handy terminal includes an operation unit 10 including a plurality of buttons, a display unit 20, a scanner unit 30, and a battery pack housing unit 40. The display unit 20 is a display device represented by an LCD. The scanner unit 30 is an existing reading device represented by a laser scanner. The battery pack housing part 40 is a part for housing a rechargeable battery pack 50 as a power source. Attachment of the battery pack 50 to the battery pack housing part 40 and removal of the battery pack 50 from the battery pack housing part 40 can be performed arbitrarily. Further, the battery pack can be arbitrarily replaced. The battery pack 50 is a general-purpose battery pack dedicated to the handy terminal.

  By pressing a power button provided on the operation unit 10, power is supplied from the battery pack 50 housed in the battery pack housing unit 40. Moreover, the battery pack 50 accommodated in the battery pack accommodating part 40 can be charged by connecting the handy terminal to an AC power outlet via an AC adapter (not shown). The display unit 20 displays the remaining battery level of the battery pack 50 attached to the battery pack housing unit 40. There are two display formats for displaying the remaining battery level: a precise remaining battery level display (first display format) and a simple remaining battery level display (second display format). The handy terminal of the present embodiment displays the remaining battery level in the first display format after the battery is fully charged until the battery pack replacement is detected, and the battery in the second display format after the battery replacement. It is characterized in that the remaining amount is displayed.

  Hereinafter, the configuration of the handy terminal of the present embodiment will be described in detail with reference to FIG.

  The main part of the handy terminal of the present embodiment includes a charging circuit 1, a gauge IC 2, a power supply circuit 3, a microcomputer 4, a battery replacement detection unit 5, a main CPU 6, and a storage device 7. When power is supplied from the AC power supply via the AC adapter, the charging circuit 1 supplies a charging current to the battery pack 50 accommodated in the battery pack accommodating portion 40 and sends a charging start signal to the microcomputer 4. Send it out. The charging current from the charging circuit 1 is supplied to the battery pack 50 via the gauge IC 2. In addition, the charging circuit 1 can detect the full charge of the battery pack 50, and sends a signal (full charge detection signal) indicating that to the microcomputer 4 when full charge is detected. Full charge is determined by whether or not a full charge condition is satisfied (specifically, two conditions where the voltage is equal to or higher than the specified voltage and the current is equal to or lower than the specified current).

  The gauge IC 2 includes a terminal with which the battery terminal of the battery pack 50 housed in the battery pack housing portion 40 is in contact, and supplies the charging current from the charging circuit 1 to the battery pack 50 through the terminal. A discharge current is supplied from the battery pack 50. The discharge current from the battery pack 50 is supplied to the power supply circuit 3 via the gauge IC 2. The gauge IC 2 can measure the voltage, current, and current integration of the battery pack 50, holds the measurement result in a nonvolatile memory provided therein, and sends it to the microcomputer 4.

  In the current integration measurement, a first integration process for integrating the time integral value of the charging current measured at a constant time interval and a second integration process for integrating the time integral value of the discharge current measured at a constant time interval. And done. The gauge IC 2 is an integrated value (corresponding to the discharge amount) obtained by the second integration process from the current capacity at the time of full charge set by the microcomputer 4 until the battery is replaced after full charge. The value obtained by subtracting is output.

  The battery replacement detection unit 5 is a part that detects whether or not the battery pack 50 has been replaced. This battery replacement detection part 5 can be comprised from the sensor which detects opening / closing of the lid | cover provided in the battery pack accommodating part 40, for example. In this case, regardless of whether the battery pack 50 is actually replaced, the battery replacement detection unit 5 considers that the battery has been replaced when the sensor detects that the lid has been opened and closed. A signal indicating this (battery replacement detection signal) is sent to the microcomputer 4.

  The microcomputer 4 has a function of estimating the remaining battery level of the battery pack 50 by controlling the gauge IC 2. There are two types of estimation of the remaining battery level: estimation of the remaining battery level in the first display format and estimation of the remaining battery level in the second display format. From the time when the full charge detection signal is received from the charging circuit 1 to the time when the battery replacement detection signal is received from the battery replacement detection unit 5, the remaining battery level is estimated in the first display format. After receiving the battery replacement detection signal from the battery replacement detection unit 5, the remaining battery level is estimated in the second display format.

  In the estimation of the remaining battery level in the first display format, the microcomputer 4 sets a predetermined current capacity at full charge for the gauge IC 2 simultaneously with reception of the full charge detection signal. Then, the first battery remaining amount is estimated based on the output of the gauge IC 2 (a value obtained by subtracting the integrated value obtained by the second integrating process from the current capacity at the time of full charge). The first battery remaining amount estimated in this way is supplied to the main CPU 6 together with the corresponding display format information.

  On the other hand, in the estimation of the remaining battery capacity in the second display format, the microcomputer 4 uses a two-dimensional map of preset current-voltage characteristics, the battery voltage and discharge current measured by the gauge IC 2, and the discharge current. The amount of discharge is obtained from each of the integrated values. Then, the second battery remaining amount is estimated based on the obtained discharge amount and the current capacity at the time of full charge. The second battery remaining amount estimated in this way is supplied to the main CPU 6 together with information on the corresponding display format. The two-dimensional map is stored in advance in a memory that can be read by the microcomputer 4. This memory may be the storage device 7 or another memory (not shown).

  The storage device 7 includes a semiconductor memory, and stores a program for operating the handy terminal, data necessary for processing, and the like. The main CPU 6 reads and executes the program stored in the storage device 7 to control the operation of each part of the handy terminal. When information on the remaining battery level and the display format is supplied from the microcomputer 4, the main CPU 6 causes the display unit 20 to display the supplied remaining battery level in a corresponding display format. The main CPU 6 is supplied with a full charge detection signal from the charging circuit 1 via the microcomputer 4. When the main CPU 6 receives the full charge detection signal, the display unit 20 indicates that charging has been completed. Alternatively, the user is notified by output means such as an LED provided separately.

  Next, the operation of the handy terminal of this embodiment will be described. Since the basic operations of the handy terminal, such as reading data using the scanner unit and transferring data to a computer terminal by a communication function (not shown), are well known, explanation of such basic operations is omitted here. Only the charging and battery remaining amount display operations that are characteristic will be described.

(1) Charging When the user connects the handy terminal to an AC power source via an AC adapter, power is supplied from the AC power source to the charging circuit 1 via the AC adapter. The charging circuit 1 starts charging the battery pack 50 when power is supplied from the AC power source. When the charging of the battery pack 50 is completed, the charging circuit 1 sends a full charge detection signal to the microcomputer 4. The microcomputer 4 sends the full charge detection signal received from the charging circuit 1 to the main CPU 6. The main CPU 6 that has received the full charge detection signal notifies the user that the charging has been completed by the display unit 20 or an output means such as an LED provided separately. The user recognizes that the charging is completed by this charging completion notification, and removes the handy terminal from the AC adapter.

(2) Battery remaining amount display By pressing the power button provided on the operation unit 10, power supply by the battery pack 50 is started, and the remaining battery amount is estimated by the microcomputer 4, and the estimated value is obtained. The remaining battery level is displayed on the display unit 20 by the main CPU 6. FIG. 3 shows an example of the battery remaining amount display operation in the control unit including the microcomputer 4 and the main CPU 6.

  First, the microcomputer 4 determines whether or not a full charge detection signal is supplied from the charging circuit 1 (step S10). If this determination is “No”, Step S10 is repeated. If “Yes”, then the microcomputer 4 sets a predetermined current capacity at the time of full charge for the gauge IC 2 and also an integrated amount (at the time of full charge) which is the output of the gauge IC 2. The first battery remaining amount is estimated based on the current capacity obtained by subtracting the integrated value obtained in the second integrating process (step S11). Then, the main CPU 6 displays the estimated first battery remaining amount on the display unit 20 in the first display format (step S12).

  After the process of step S12, the microcomputer 4 determines whether or not a battery replacement detection signal is supplied from the battery replacement detection unit 5 (step S13). If the determination is “No”, the process returns to the process of step S11. If “Yes”, the microcomputer 4 refers to a two-dimensional map that represents the relationship between the battery voltage and the discharge amount at each of a plurality of different current values, and the battery voltage measured by the gauge IC 2 and A discharge amount is obtained from the discharge current, and the second battery remaining amount is estimated based on the discharge amount and the current capacity at full charge (step S14). Then, the main CPU 6 displays the estimated second battery remaining amount on the display unit 20 in the second display format (step S15).

  After the process of step S15, the microcomputer 4 determines whether or not a charge start signal is supplied from the battery replacement detection unit 5 (step S16). If “No” is determined in this determination, the process returns to step S14. If “Yes” is determined, the process returns to step S10.

  According to the above-described battery remaining amount display operation in the handy terminal of the present embodiment, a precise battery remaining amount is displayed in the first display format for a fully charged battery pack. The battery remaining amount display in the first display format can be displayed in units of 1%. A specific process for displaying in units of 1% will be briefly described below.

  The current capacity at full charge is 1700 mAh. When the microcomputer 4 receives the full charge detection signal, the microcomputer 4 sets 1700 mAh as the current capacity at the time of full charge for the gauge IC 2. The gauge IC2 outputs an integrated amount obtained by subtracting the time integration value of the discharge current obtained at a constant time interval from the current capacity of 1700 mAh. Here, the time integration value when 1 mA of current flows for 1 hour is 1 mAh. Similarly, the time integration value when a current of 60 mA flows for 1 minute is also 1 mAh. The time integral value (mAh) is obtained by converting the average current in a certain period (usually 1 minute or less) into “mAh”.

  The microcomputer 4 obtains the remaining battery level from the integrated amount from the gauge IC 2 and the current capacity of 1700 mAh by the following formula.

In this calculation formula, 1700 mAh is assumed to be a battery remaining amount of 100%, and a margin of 10% is taken to absorb variations. When the integrated amount is 170 mAh, the remaining battery level is 1%, and when the integrated amount is 1700 mAh, the remaining battery level is 100%. In this way, accurate display is possible by obtaining the remaining battery level in units of 1%.

  FIG. 4 is a schematic diagram showing a display example of the remaining battery level in the first display format. In this example, the black area of the gauge in the form of a battery represents the remaining battery capacity. On the gauge, the remaining battery level is displayed in units of 1%. The user can accurately determine the battery replacement time from the remaining battery level displayed in units of 1%, and can use the battery pack until the remaining battery level is almost reached.

  Further, according to the battery remaining amount display operation in the handy terminal of the present embodiment, when the battery pack is replaced, the remaining battery amount is accurately displayed in the second display format for the replaced battery pack. The battery remaining amount display process in the second display format will be briefly described below.

  FIG. 5 shows an example of a two-dimensional map. The vertical axis represents voltage, and the horizontal axis represents discharge amount. The discharge amount is obtained from the integrated value of the discharge current, and has the same meaning as the remaining battery capacity (remaining battery capacity). The solid line is a graph showing the relationship between the battery voltage and the discharge amount when the discharge current is 0.34 A, and the broken line is the graph showing the relationship between the battery voltage and the discharge amount when the discharge current is 1.7 A.

  When the measurement result that the battery voltage is 3.75 V and the discharge current is 1.7 A is obtained at the gate IC 2, the microcomputer 4 refers to the graph regarding 1.7 A on the two-dimensional map, and the discharge amount is calculated from the battery voltage. Acquire 600 mAh. Then, the microcomputer 4 obtains a value (remaining capacity) obtained by subtracting the discharge amount 600 mAh from the current capacity 1700 mAh at the time of full charge, and supplies the discharge amount or the ratio (%) of the remaining capacity to the current capacity to the main CPU 6. Send it out.

  The main CPU 6 displays a battery remaining amount gauge in a plurality of stages based on the remaining battery amount (%) supplied from the microcomputer 4. FIG. 6 is a schematic diagram illustrating a display example of the remaining battery level in the second display format. A battery-shaped gauge is displayed in four stages. In FIG. 6, the gauge shown at the top indicates a state where the remaining battery level is 75% or more. The second gauge indicates a state where the remaining battery level is less than 75% and 50% or more. The third gauge indicates a state where the remaining battery level is less than 50% and 25% or more. The fourth gauge indicates a state where the remaining battery level is less than 25%. The remaining amount displayed at each stage is equal. For example, when the battery pack can be used for 4 hours from full charge, the battery pack is reduced by one step every hour. Therefore, the user can grasp the remaining battery level accurately to some extent, and can use the battery pack until the remaining battery level is almost marginal. Note that in the case of gradual display of gauges often found on mobile phones, it is difficult to accurately grasp the remaining battery level because the remaining amount displayed in each step is different.

  The two-dimensional map shown in FIG. 5 shows the relationship between the battery voltage and the discharge amount for two current values. Usually, a two-dimensional map for a plurality of different current values is used. Further, since the relationship between the battery voltage and the discharge amount also changes depending on the temperature, a two-dimensional map may be created for each of a plurality of different temperatures. In this case, the temperature is measured in addition to the voltage and current with the gauge IC, and the discharge amount is obtained with reference to a two-dimensional map of the measured temperature.

  In the example of FIG. 6, the remaining battery level is displayed at four levels, but the number of stages is not limited to this. Any number of stages may be used as long as the remaining battery level can be accurately displayed. However, since the estimation of the remaining battery level in the second display format includes a certain amount of error, it is desirable to display in increments of 25%.

  In addition, the replacement of the battery pack is detected based on the opening / closing of the lid of the battery pack housing 40, but any method may be used as long as the replacement of the battery can be detected. For example, it can be detected by measuring the voltage of the battery pack 50. In this case, the voltage measurement result is supplied from the gauge IC 2 to the battery replacement detection unit 5. Then, the battery replacement detection unit 5 is measured by the gauge IC 2 immediately after being turned on by the power button and the battery voltage measured by the gauge IC 2 just before being turned off by the power button of the operation unit 10. It is determined that the battery has been replaced when the difference from the battery voltage is equal to or greater than a predetermined value. Here, the predetermined value is a value that can reliably detect battery replacement.

  In addition, when replacing the battery pack, since the power is turned off with the power button, power supply by the battery pack is stopped. For this reason, in the handy terminal of the present embodiment, power is supplied from the built-in battery so that the replacement of the battery pack can be detected even after the power is turned off.

  In addition, if a handy terminal that has been fully charged and has been used for a certain period of time is connected again to the AC power supply via the AC adapter and recharged, and the recharge is completed before it is fully charged, the The amount of charge by charging is added to the integrated amount. Specifically, in the gauge IC 2, the charge amount for recharging is calculated by the first integration process described above, and the calculated charge amount is added to the remaining battery level immediately before the start of recharging.

  The handy terminal of this embodiment described above is an example of the present invention, and the configuration and operation thereof can be changed as appropriate without departing from the spirit of the present invention.

It is a block diagram which shows the structure of the principal part of the handy terminal which is one Embodiment of this invention. It is an external view of the handy terminal shown in FIG. It is a flowchart figure which shows the display operation of the battery remaining amount performed in the handy terminal shown in FIG. It is a schematic diagram which shows an example of the display of the battery remaining charge by a 1st display format. It is a characteristic view which shows an example of a two-dimensional map. It is a schematic diagram which shows an example of the display of the battery remaining charge by a 2nd display format.

Explanation of symbols

1 Charging circuit 2 Gauge IC
3 Power Circuit 4 Microcomputer 5 Battery Replacement Detection Unit 6 Main CPU
7 Storage Device 10 Operation Unit 20 Display Unit 30 Scanner Unit 40 Battery Pack Storage Unit 50 Battery Pack

Claims (8)

A display unit;
An accommodating part for accommodating a replaceable battery pack;
When power is supplied from the outside, the charging unit that charges the battery pack stored in the storage unit and detects whether or not the battery pack is fully charged;
A battery replacement detection unit that detects whether or not the battery pack stored in the storage unit has been replaced;
A measurement integration unit that measures at least the battery voltage and discharge current of the battery pack at regular time intervals and integrates the measured discharge current;
Control means for estimating the battery remaining amount of the battery pack accommodated in the accommodating portion on the basis of a preset current capacity at the time of full charge and displaying on the display portion;
The control means includes
From the time when full charge is detected by the charging unit to the time when battery replacement is detected by the battery replacement detection unit, the integrated value of the current capacity and the discharge current measured by the measurement integration unit the battery level is also displayed in the first display format I estimates based on bets,
After the battery replacement was detected by the battery replacement detection unit, the measurement integration unit measured with reference to characteristic data representing the relationship between the battery voltage and the discharge amount at each of a plurality of different current values. determine the amount of discharge from the battery voltage and discharge current, to display a different second display format than the first display format I also estimate the remaining battery capacity on the basis of said current capacity and the discharge amount determined the A portable information processing terminal characterized by that.   The battery replacement detection unit includes a sensor that detects opening / closing of the lid of the housing unit, and determines that the battery pack has been replaced when the opening / closing of the lid is detected by the sensor. The portable information processing terminal described. A power button for turning on / off power supply by the battery pack;
The battery replacement detection unit includes a battery voltage measured by the measurement integration unit immediately before being turned off by the power button, and a battery measured by the measurement integration unit immediately after being turned on by the power button. The portable information processing terminal according to claim 1, wherein it is determined that the battery pack has been replaced when a difference from the voltage is equal to or greater than a predetermined value. The measurement integrating unit is configured to measure the charging current supplied from the charging unit to the battery pack at regular time intervals and perform the integration.
If the charging unit performs recharging of the battery pack after detecting full charge, and the charging unit does not detect full charging by the recharging, the control unit is connected to the measurement integrating unit during the recharging. 2. The portable information processing terminal according to claim 1, wherein a charge amount is obtained from an integrated value of the charging current measured in this manner, and the charge amount is added to a remaining battery level estimated after the recharging. A method of displaying a remaining battery level of the battery pack, which is performed in a portable information processing terminal including a replaceable battery pack,
A first step of charging the battery pack;
A second step of detecting whether or not the battery pack is fully charged by the charging;
A third step of detecting whether or not the battery pack has been replaced;
A fourth step of measuring at least the battery voltage and discharge current of the battery pack at regular time intervals and integrating the measured discharge current;
After the full charge is detected in the second step until the battery replacement is detected in the third step, the current capacity obtained at the time of full charge and the fourth step are obtained. a fifth step of displaying in a first display format I also estimate the remaining battery capacity based on the integrated value of the resulting discharge current,
After battery replacement is detected in the third step, the battery voltage measured in the fourth step with reference to the characteristic data representing the relationship between the battery voltage and the discharge amount at each of a plurality of different current values. and determine the discharge amount from the discharge current, the sixth to be displayed in a different second display format than the first display format I also estimate the remaining battery capacity on the basis of said current capacity and the discharge amount determined the The battery remaining amount display method including these steps.   The battery remaining amount display method according to claim 5, wherein the third step includes a step of determining that the battery has been replaced when a lid of a portion that houses the battery pack is opened and closed. The third step includes
Measuring a first battery voltage immediately before the power supply by the battery pack is turned off;
Measuring a second battery voltage immediately after power supply by the battery pack is turned on;
6. The battery remaining amount display method according to claim 5, further comprising: determining that the battery has been replaced when a difference between the first and second battery voltages is equal to or greater than a predetermined value. A seventh step of measuring and integrating the charging current supplied to the battery pack at regular time intervals;
An eighth step of recharging the battery pack after full charge is detected in the second step;
A ninth step of detecting whether or not the battery pack is fully charged by the recharging;
When full charge is not detected in the ninth step, the charge amount is obtained from the integrated value of the charge current obtained in the seventh step, and the charge amount is added to the remaining battery level estimated after the recharge. The battery remaining amount display method according to claim 5, further comprising: a tenth step.

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