JP7685477B2 - Portable test meter monitors backlight battery depletion - Google Patents

Description

This application relates generally to the field of test meters, and more specifically to portable test meters used for periodic monitoring of subjects, and related methods for monitoring the depletion of batteries used in the portable test meters.

Handheld devices such as portable test meters typically require a display to communicate the results of a test measurement to a user of the test meter. Such displays may include a backlight for ease of reading in low light conditions. Portable test meters that are compact, lightweight, and long lasting without the need for frequent battery changes are desirable.

Some technologies, such as thin film transistor (TFT) display technology, offer enhanced color graphics that are desirable to users. However, these displays may be completely unreadable without a backlight and are not suitable for use in portable test meters that operate for weeks or months without a battery change because the backlight cannot be disabled to conserve power. Thus, such displays, which require constant backlighting, are typically not utilized or considered for use in such portable test meters.

Furthermore, displays commonly used in test instruments are passive liquid crystal displays (LCDs), which can still be read without an active backlight. Therefore, existing architectures of portable test instruments do not take into account the practical problems encountered in portable test instruments having TFT display screens. This requires enhanced monitoring and management of the backlight subsystem to prevent unpredictable power losses to the test instrument.

Furthermore, commonly used battery depletion detection algorithms can only look at the battery voltage before boot-up. In this case, the effects of the battery's internal resistance, ionic mobility, and temperature are not taken into account. However, such simple tests work, but only for batteries that are subject to a relatively small and steady current drain.

So that the features of the present invention can be understood, a detailed description can be obtained by reference to specific embodiments, some of which are illustrated in the accompanying drawings. It should be noted, however, that the drawings only illustrate certain embodiments and therefore should not be considered as limiting the scope of the disclosed subject matter, as it encompasses other embodiments. The drawings are not necessarily to scale, and the emphasis is generally on illustrating the features of particular embodiments. In the drawings, like numerals are used to denote like parts throughout the various views.

1 illustrates a rear view of a partially disassembled portable test meter according to an embodiment described herein. 1 illustrates a front view of a portable test meter according to an embodiment described herein. FIG. 1B is a block diagram of a controller used and powered by the portable test meter of FIG. 1A. FIG. 2B is a plan view of a circuit board containing electrical components of the portable test meter of FIGS. 1A and 2A. 1B shows a schematic diagram of a backlight battery and a main battery connected within the portable test meter of FIG. 1A. 1 illustrates a backlight driver circuit having a battery monitoring circuit according to an embodiment described herein for use in a test meter. 1 illustrates the voltage recovery characteristics of a battery intended for use as a backlight battery in a test meter according to embodiments described herein. 1 illustrates the voltage recovery characteristics of a battery intended for use as a backlight battery in a test meter according to embodiments described herein. A method for monitoring the condition of a backlight battery, such as a backlight battery having the characteristics shown in FIGS. 5A-5B, for use in a portable test meter according to aspects described herein is shown.

The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. The detailed description illustrates the principles of the invention by way of example, not by way of limitation. The description clearly enables one skilled in the art to make and use the invention and describes several embodiments, applications, variations, alternatives and uses of the invention, including what is presently believed to be the best mode of carrying out the invention.

As used herein, the terms "about" or "approximately" with respect to any numerical value or range thereof indicate the appropriate tolerances that allow a portion or collection of components to function for the intended purpose described herein. Additionally, as used herein, the terms "patient," "host," "user," and "subject" refer to any human or animal subject, and are not intended to limit the use of the systems or methods to humans, although use of the subject technology with human patients represents a preferred embodiment.

This disclosure relates in part to portable test meters, such as those used to periodically measure a subject's blood glucose level. Some of these test meters include a main or primary battery that electrically powers a controller and a display included in the test meter, along with any measurement subsystems, such as electrochemical test circuitry for monitoring blood glucose. For portable test meters with TFT or similar type displays, there is an additional need to power the backlight of the display. Thus, the test meter may further include a dedicated backlight battery, and may provide enhanced battery monitoring to facilitate replacement of the backlight battery before it becomes depleted. More specifically, the main battery may be used to power the test meter's controller, display logic, and any measurement subsystems, and the dedicated backlight battery may be used only to power the backlight. Such a configuration allows the use of TFT displays in portable test meters, despite the problem that TFT displays require a backlight to be viewed. In one embodiment, the footprint of the portable test meter is reduced by using a conventional coin cell battery as the dedicated backlight battery. The reason is that coin cells, which are not normally used for backlighting, work in a non-traditional way as described in this specification.

Additionally, coin cell batteries, such as CR2032 lithium batteries, have been commonly used in portable test meters, but are not rated for use in high power consumption components such as backlights. However, the techniques described herein allow the use of these common batteries because they take advantage of the specific usage patterns of portable test meters, such as those used regularly to measure blood glucose for diabetic patients.

Generally speaking, according to one embodiment, a portable test meter is provided. The portable test meter includes a means for monitoring a backlight battery, such as a battery monitoring circuit. The test meter includes a housing that holds a controller for periodically measuring a blood glucose level of a subject. The test meter further includes a display, such as a TFT display having a backlight, and a circuit for monitoring a dedicated backlight battery. The monitoring circuit is used to measure the off-time of the meter and compare it to a predetermined recovery time of the backlight battery. If the off-time of the meter is greater than the predetermined recovery time of the backlight battery, the voltage of the backlight battery is measured at a predetermined time after the backlight is energized and the measured voltage is compared to a first predetermined voltage that exceeds a threshold voltage of the backlight battery. If the measured voltage is less than the first predetermined voltage, the measured voltage is compared to a second predetermined voltage between the first predetermined voltage and the threshold voltage. If the measured voltage is less than the second predetermined voltage, a low battery warning is displayed.

In another embodiment, the present disclosure discloses a method for monitoring the status of a backlight battery in a portable test meter. The test meter includes a meter housing that holds a number of components, including a controller, and a display is provided in the meter housing. The display includes a TFT screen and a backlight. The backlight is powered by a backlight battery. According to the method, the off time of the meter is measured and compared to a predetermined recovery time of the backlight battery. If the off time of the meter is greater than the predetermined recovery time of the backlight battery, the voltage of the backlight battery is measured at a predetermined time after the backlight is energized and the measured voltage is compared to a first predetermined voltage that exceeds a threshold voltage of the backlight battery. If the measured voltage is less than the first predetermined voltage, the measured voltage is compared to a second predetermined voltage between the first predetermined voltage and the threshold voltage. If the measured voltage is less than the second predetermined voltage, a low battery warning is displayed.

The above-described embodiments are intended to be merely illustrative. Other suitable embodiments will be readily apparent from the following discussion that are within the intended scope of the disclosed subject matter.

Next, we will explain a specific example of the work. First, we will explain the portable test and measurement device and the battery monitoring technology in relation to Figures 1 to 6.

1A shows a rear view of the portable test meter 10 defined by a meter housing 11 configured and sized to hold a number of components. The meter housing 11 has an interior. These components include a controller 38 (see FIG. 2A), a main battery 50, and a backlight battery 52. As shown in FIG. 1B, the display 14 according to this embodiment includes a thin film transistor (TFT) screen and backlight and is located on the front side of the portable test meter 10'. In one example of operation, the main battery 50 powers the controller 38 as well as the TFT display logic, while the backlight battery 52 powers only the display backlight.

In some configurations, the backlight may be a light emitting diode (LED) or an array of LEDs, where the array may include 1-50 LEDs. In other embodiments, the backlight may be a fluorescent device, an electroluminescent device, an organic light emitting diode (OLED), or any other light source that may be disposed within the housing 11 of the test meter 10, 10' of FIGS. 1A and 1B.

FIG. 1B illustrates a diabetes management system that includes a portable test meter 10' and a biosensor in the form of a glucose test strip 62. The portable test meters 10, 10' have different physical appearances but generally operate in the same manner. It is noted that the meter (meter unit) may also be referred to as an analyte measurement management unit, glucose meter, meter, or analyte measurement device (not shown). In one embodiment, the meter unit may be combined with an insulin delivery device, additional analyte testing devices, and drug delivery devices. The meter unit may be connected to a remote computer or server via a cable or suitable wireless technology such as, for example, GSM, CDMA, Bluetooth, WiFi, etc. Such a management system is described in more detail in U.S. Patent No. 8,709,232, issued April 29, 2014, entitled "Analyte measurement technique and system," which is incorporated herein by reference in its entirety.

Returning to FIG. 1B, the glucose meter or meter unit 10' is defined by a housing 11 having a number of user interface buttons (16, 18, 20) disposed on a facing surface of the housing 11. A display 14 is provided in addition to a test strip port opening 22 configured to receive a biosensor (test strip 62). The user interface buttons (16, 18, 20) may be configured to allow data entry, menu navigation, and command execution. The user interface button 18 may be in the form of a two-way toggle switch. The number and orientation of the user interface buttons may take on various configurations, with the three interface buttons depicted being one example. The data may include values representative of analyte concentrations and/or information related to the individual's daily living. The information related to daily living may include the individual's diet, medication status, medical examination attendance, health status, and activity level. The electronic components of the portable test meter 10, 10' may be located on a circuit board 34 (FIG. 2B) disposed within the meter housing 11, 11'.

FIG. 2A is a partial block diagram of a portable test meter, showing a controller 38 connected to a power source 220. The controller 38 includes a central processing unit (CPU) 212, a random access memory (RAM) 214, an analog-to-digital converter (ADC) 216, and a general-purpose input/output (GPIO) 218. The ADC 216 is connected to a backlight battery monitoring circuit and can be used to measure its voltage. The GPIO 218 can communicate with the display to turn on the backlight 60 (see FIG. 3) or with the battery monitoring circuit (see FIG. 4).

2B illustrates (simplified) the electronic components located on the top surface of the circuit board 34 located within the test meter 10 of FIG. 1A. These electronic components include the strip port connector 22, the operational amplifier circuitry 35, the controller 38, the display connector 14a, the non-volatile memory 40, the clock 42, and the first wireless module 46. On the bottom surface of the circuit board 34, the electronic components may include a battery connector (not shown) and a data port 13. The controller 38 may be electrically connected to the strip port connector 22, the operational amplifier circuitry 35, the first wireless module 46, the display 14, the non-volatile memory 40, the clock 42, at least one battery, the data port 13, and the user interface buttons 16, 18, 20.

The op-amp circuit 35 may include two or more op-amps configured to provide a portion of the potentiostat and current measurement functions. The potentiostat function may refer to the application of a test voltage between at least two electrodes of a test strip used in conjunction with a test meter. The current function may refer to the measurement of a test current resulting from the applied test voltage. The current measurement may be performed using a current-to-voltage converter. The controller 38 may be in the form of a mixed signal microprocessor (MSP), such as, for example, a Texas Instrument MSP430. The TI MSP430 may also be configured to perform a portion of the potentiostat and current measurement functions. Additionally, the controller 38 may include volatile and non-volatile memory. In another embodiment, many of the electronic components may be integrated with the controller in the form of an application specific integrated circuit (ASIC).

The test strip port connector 22 may be configured to form an electrical connection to a test strip, such as the test strip 62. The display connector 14a may be configured to attach to the display 14. The display 14 may be in the form of a liquid crystal display to report the measured glucose level and to facilitate the input of lifestyle related information using the interface buttons 16, 18, 20. More specifically, and according to the present embodiment, the display 14 includes a backlight. The data port 13 may receive a suitable connector attached to a connection lead (not shown), thereby linking the test meter 10 to an external device, such as a personal computer. The data port 13 may be any port that allows for the transmission of data, such as, for example, a serial, USB, or parallel port. The clock 42 may be configured to keep a current time associated with the geographic region in which the user is located and to measure time, as will be described in more detail below. The test meter may be configured to be electrically connected to a power source, such as, for example, at least one included battery, as shown according to FIG. 3.

FIG. 3 shows a schematic diagram of further details of the power supply configuration for the test meter 10 of FIG. 1. In this configuration, the controller 38 is connected to a main battery 50 for powering the controller 38. A backlight battery 52 is utilized to power the backlight 60 of the display 14 via a backlight driver circuit 54.

Figure 4 illustrates a backlight driver circuit 410 according to an embodiment as used with a battery monitor circuit 420. The exemplary backlight driver circuit 410 employs a switch-mode boost regulator operating in a constant current configuration. The driver circuit 410 outputs to an LED backlight via LED_A and LED_K. The LED current is controlled by resistor R32. In such a case, a reference voltage, for example 500 mV, can be maintained at pin FB of U10 to provide an LED drive current of about 10 mA. The battery monitor circuit 420 measures the voltage VBAT2 via an analog-to-digital converter (ADC). For example, to facilitate the backlight battery measurement, the controller can pull the signal EN_VBAT2_MEAS to a low potential, thus turning on MOSFET Q4. This allows the voltage from BT2 to reach the voltage divider created by R34/R38. The ratio of these two resistors divides the BT2 voltage by a factor of 1.7, which is then fed to the ADC. The voltage divider ensures that the BT2 voltage does not saturate the ADC input.

Figures 5A-5B show the electrochemical voltage recovery characteristics of a lithium coin backlight cell according to embodiments defined herein. For example, if the backlight cell is loaded to 0.8V, when the load is removed, Figure 5A shows that the voltage begins to recover to over 2V after about 60 seconds. However, recovery to 99% of the nominal cell voltage of, for example, 3V, may take about 3 hours, as shown in Figure 5B.

For example, a particular battery model may be selected for use in a portable test meter as a backlight battery. Such a battery can be characterized through factory testing to determine the amount of time it takes for the battery to return to electrochemical equilibrium after being withdrawn over a period of typical usage of the portable test meter. For a portable glucose test meter that is typically used for approximately 2-5 minutes at a time, 3-4 times per day, a battery cycle can be characterized with a full withdrawal of 5 minutes to determine the time required for recovery.

In particular, the lithium coin cell battery displaying the characteristics of FIGS. 5A-5B is not ideal for powering the backlight battery of a device that is operated continuously for relatively long periods of time. However, because test meters such as glucose meters are typically used for relatively short periods of time several times per day during the testing process, lithium coin cells can be used as the backlight battery in such meters by employing monitoring techniques such as those described herein. These monitoring techniques allow for the detection of depleted batteries and their timely replacement.

In addition to recovery time characteristics, a battery may exhibit voltage degradation when stored at temperatures outside its normal operating range. In such cases, although the battery is well below its nominal operating temperature, the techniques described herein may account for the temperature being outside the operating range by refraining from issuing a depleted battery message during such cycles.

FIG. 6 illustrates a method 600 for monitoring the status of the backlight battery 52 of the portable test meter 10, 10' of FIG. 1A or 1B when using a backlight battery having similar characteristics as those of FIG. 5A and 5B. As previously discussed, test meters, such as glucose meters, include periodic measurements taken during a 24-hour period based on meals and other events (exercise, sleep, etc.). Thus, the test meter is not powered at all times, and glucose measurements may be obtained several times during a given 24-hour period, with measurements often taking less than a minute. For purposes of the present invention and for determining backlight battery depletion, it has been found that the off time of the test meter is an important factor that can be utilized to determine whether the backlight battery is depleted. In describing method 600, a specific working example will be provided for illustrative purposes only.

In one embodiment, the method 600 at block 610 measures the off time of the meter and compares the measured off time of the meter to a predetermined recovery time of the backlight battery. For example, the controller 38 may store a backlight usage record in non-volatile memory. In the illustrative specific working example followed here with respect to FIG. 6, the record may indicate that the backlight was last energized at 1:08 PM on day X. Then, the next time the meter is turned on, the meter may obtain the current system time from the controller's on-board clock. In a specific working example, the current system time may be 5:28 PM on day X. The controller may then determine the off time by subtracting the last energization time from the current system time, which in this specific working example is 4 hours and 20 minutes.

To accurately measure whether a test meter's contained battery is depleted, the measurement is most accurate when the battery is allowed to recover from periodic cycling. In such a case, method 600 at block 620 determines whether the meter's off time is greater than a predetermined recovery time for the backlight battery. In a specific working example, a lithium coin battery may require a period of four hours to recover, so in this example, the controller may compare the actual off time to the recovery time of four hours and proceed down the YES branch of block 620. Alternatively, if the battery was not able to fully recover for the full four hours at block 620, method 600 proceeds to block 690 and no warning message is displayed. In such a case, the meter may proceed with a main meter routine and a test, such as a blood glucose test, may be performed.

In another example, a battery may require anywhere from 10 minutes to 12 hours to recover. The recovery time of a particular battery model used in a particular test meter may be characterized and an appropriate value of the recovery time may thus be predetermined. Characterization of the battery's recovery time may be done by controlled testing with N battery replicas and measuring the battery's internal voltage with a voltmeter, as described with respect to Figures 5A-5B.

Continuing, the method 600 at block 630 turns on (energizes) the backlight of the test meter and measures the voltage of the backlight battery at a predetermined time after the backlight is energized. The predetermined time may be selected to allow the backlight to be fully energized before taking the measurement. In a specific working example, the battery monitoring circuit 410 may read the voltage after the predetermined time and the controller may store the voltage in non-volatile memory. The predetermined time may be selected by controlled testing using a high speed voltmeter in a controlled environment to monitor the backlight battery voltage during the first few seconds of backlight operation to determine how much time must pass for the voltage drop to stabilize.

Next, the method 600 at block 640 compares the measured voltage to a first predetermined voltage that exceeds a threshold voltage of the backlight battery. The first predetermined voltage may be selected as a voltage high enough that there is little or no likelihood that the backlight battery is near depletion. Conversely, the threshold voltage may be selected as the minimum possible voltage required to energize the backlight. In one embodiment, the threshold voltage may be 0.8V and the first predetermined voltage may be 2.5V (the voltage of a fresh battery).

At block 650, method 600 determines whether the measured voltage is less than a first predetermined voltage. If the measured voltage is greater than or equal to the first predetermined voltage, method 600 proceeds to block 690 and no warning is displayed because the backlight battery is not close to being depleted. In one example, the first predetermined voltage may be set equal to the full voltage of the newly installed battery.

If the method 600 at block 650 determines that the measured voltage is less than the first threshold voltage, the method 600 proceeds to block 660 and compares the measured voltage to a second predetermined voltage. The second predetermined voltage is between the first predetermined voltage and the threshold voltage. The second predetermined voltage may be selected through controlled testing of N (e.g., N=100) replicate test meters and batteries. The second predetermined voltage represents a voltage at which the battery is close enough to being depleted that user intervention is required. For example, the second predetermined voltage may be determined through controlled testing to a point where a certain small number of typical meter tests may be performed before the battery is completely depleted, e.g., 1 to 5 tests. In one example, the second predetermined voltage may be between 1.0V and 1.2V.

At block 670, the method 600 determines whether the measured voltage is less than the second predetermined voltage. If the measured voltage is not less than the second predetermined voltage, the method proceeds to block 690 and no warning is displayed.

Conversely, if the measured voltage is less than the second predetermined voltage, the method proceeds to block 690 where a low battery warning or message is displayed on the meter. In one example, the low battery message may be continuously displayed on the meter as a low battery icon. In another example, the meter may require acknowledgment of the low battery warning before allowing a test to run. In a further example, the low battery warning may display the number of test cycles remaining on the meter. In yet another example, the low battery warning may be escalated or repeated based on how few typical tests are remaining.

In another embodiment, the method may measure a second voltage of the backlight battery at a second predetermined time. For example, the second voltage may be measured between 1 second and 1000 seconds after measuring the first voltage. The measured second voltage may be used to determine the voltage drop of the battery that occurs during the predetermined time after the backlight is energized. As the backlight battery becomes depleted, this voltage drop increases with each use cycle. In an example using a low capacity battery to power the backlight, such a battery may power the backlight for a certain duration before needing to be turned off for a recovery cycle. Thus, if the backlight is powered for more than a certain time interval and cannot be recovered, the meter may determine that the battery is only temporarily depleted, rather than permanently depleted. Again, the acceptable on-time of such a battery may be characterized by controlled testing of N replicate meters with the battery.

In particular, method 600 described above with respect to blocks 610-680 is typically performed before a user of the meter performs a test on the meter. Thus, the user may receive a backlight battery warning and may decide at that time to forgo performing a test, such as a self-monitored blood glucose test, and immediately replace the backlight battery. In another example, the user may choose to perform a test first and then replace the backlight battery. In yet another embodiment, based on the battery voltage level after energizing the backlight, the controller may estimate the number of typical test cycles that may remain before the battery is no longer able to fully light the screen, and provide a warning indicating how many tests are possible before the battery is fully depleted.

In another embodiment, in addition to or instead of the battery depletion check described above, a so-called gas gauge technique can be employed in which the cumulative energy used by a battery over its life is tracked by measuring the voltage and current for each historical time interval the meter is used, starting from when a new battery is installed in the system. Such a technique, when used alone, is prone to error, since a partially charged battery may be installed in the test meter. However, when combined with the other monitoring described above, such a technique can eliminate false positives and false negatives. For example, the meter can use accumulated usage data to disable a battery depletion warning if a known new battery is installed (e.g., a smart battery with a specific identification code indicating the manufacturer).

Although the present invention has been described with respect to certain variations and exemplary drawings, those skilled in the art will recognize that the present invention is not limited to the variations or drawings described. In addition, where the methods and steps described above indicate that certain events occur in a certain order, those skilled in the art will recognize that the order of certain steps may be changed and that such changes are in accordance with variations of the present invention. Furthermore, certain of the steps may not only be performed in the order as described above, but may also be performed simultaneously in parallel processes, where possible. Therefore, to the extent there are variations of the present invention that are within the spirit of the present disclosure or equivalent to the invention found in the claims, this patent is intended to cover those variations as well.

To the extent the claims recite the phrase "at least one of" with respect to multiple elements, this is intended to mean at least one or more of the listed elements, and is not limited to at least one of each element. For example, "at least one of element A, element B, and element C" is intended to refer to only element A, or only element B, or only element C, or any combination thereof. "At least one of element A, element B, and element C" is not intended to be limited to at least one of element A, at least one of element B, and at least one of element C.

This specification uses examples to disclose the invention, including the best mode, and to enable any person skilled in the art to practice the invention, including making and using any device or system, and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that do not differ in substance from the literal language of the claims.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprise" (and any form of comprise, such as "comprises" and "comprising"), "have" (and any form of have, such as "has" and "having"), "include" (and any form of include, such as "includes" and "including"), and "contain" (and any form of contain, such as "contains" and "containing") are open-ended conjunctive verbs. It is further understood that, as a result, a method or apparatus that "comprises," "has," "includes," or "contains" one or more steps or elements retains those one or more steps or elements, but is not limited to retaining those one or more steps or elements. Similarly, a method step or apparatus element that "comprises," "has," "includes," or "contains" one or more features retains those one or more features, but is not limited to retaining those one or more features. Furthermore, an apparatus or structure that is configured in a particular way may be configured in at least that way, but not in ways that are not recited.

Corresponding structures, materials, acts, and equivalents of all means-plus-function or step-plus-function elements of the following claims are intended to include any structure, material, or act for performing a function in combination with other claim elements, if any, specifically claimed. The description set forth herein has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosed forms. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the present disclosure. The embodiments have been selected and described in order to best explain the principles and practical applications of one or more aspects described herein and to enable others skilled in the art to understand one or more aspects described herein in various embodiments with various modifications suitable for the particular use contemplated.

Claims (8)

A measuring device housing;
A controller;
a display on the meter housing, the display comprising a thin film transistor (TFT) screen and a backlight;
a backlight battery operably connected to the backlight;
a battery monitoring circuit operably connected to the controller and to the backlight battery, the battery monitoring circuit comprising:
measuring an off time of the portable test meter and comparing the measured off time of the portable test meter to a predetermined recovery time of the backlight battery;
if the off time of the portable test meter is greater than the predetermined recovery time of the backlight battery, measuring the voltage of the backlight battery at a predetermined time after energizing the backlight, and comparing the measured voltage to a first predetermined voltage that is a high voltage that is unlikely to indicate that the backlight battery is near depletion in order to enhance monitoring of the backlight battery, the first predetermined voltage being above a threshold voltage that is a minimum possible voltage required to energize the backlight of the backlight battery;
if the measured voltage is less than the first predetermined voltage, comparing the measured voltage to a second predetermined voltage, the second predetermined voltage being between the first predetermined voltage and the threshold voltage;
displaying a low battery warning if the measured voltage of the backlight battery is less than the second predetermined voltage;
Do the following:
The portable test meter further comprising a main battery operatively connected to the controller and the TFT screen, the main battery and the backlight battery being coin cells. 10. The portable test meter of claim 1, wherein the backlight battery is a lithium coin cell battery. 1. A method for monitoring a backlight battery status of a portable test meter, the portable test meter comprising: a meter housing; a controller; and a display on the meter housing, the display comprising a TFT screen and a backlight, the backlight being powered by the backlight battery, the method comprising:
measuring an off time of the portable test meter and determining if the off time is greater than a predetermined recovery time of the backlight battery;
energizing the backlight;
if the off time of the portable test meter is longer than the predetermined recovery time of the backlight battery, measuring the voltage of the backlight battery at a predetermined time after energizing the backlight;
comparing the measured voltage to a first predetermined voltage, a high voltage that is unlikely to indicate that the backlight battery is near depletion, to enhance monitoring of the backlight battery, the first predetermined voltage being above a threshold voltage that is the minimum possible voltage required to energize the backlight of the backlight battery;
if the measured voltage is less than the first predetermined voltage, comparing the measured voltage to a second predetermined voltage, the second predetermined voltage being between the first predetermined voltage and the threshold voltage;
if the measured voltage of the backlight battery is less than the second predetermined voltage, causing the TFT screen of the portable test meter to display a low battery warning;
Including,
The method, further comprising a main battery operably connected to said controller and said TFT screen, wherein said main battery and said backlight battery are coin cells. 4. The method of claim 3 , further comprising the step of displaying a low battery warning on the TFT screen of the portable test meter. The method of claim 3 , further comprising measuring a cumulative power draw of the backlight battery during a power-on operation of the backlight. The method of claim 3 further comprising measuring a temperature of the backlight battery. The method of claim 3 , wherein the backlight battery is a lithium coin cell battery. The portable test meter of claim 1, wherein the portable test meter is used to periodically measure a patient's blood glucose level.

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