System and method of measuring a battery lifetime
First Claim
1. A method for determining the time remaining until a battery reaches a first predetermined voltage reference, which represents a first end-of-life voltage, comprising the steps of:
- a) measuring the instantaneous battery voltage at predetermined time intervals to determine a rate of change in the battery voltage;
b) measuring the instantaneous battery voltage and comparing the instantaneous battery voltage measurement against the first voltage reference to provide a first voltage margin which is a voltage proportional to the difference between the instantaneous battery voltage measurement and the first voltage reference; and
c) dividing the first voltage margin obtained in step b) by the voltage rate of change obtained in step a) to provide a first battery condition, which is a period of time proportional to the time remaining until the instantaneous battery voltage measured in step b) approximately equals the first voltage reference, whereby the remaining useful life of the battery is determined.
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Accused Products
Abstract
A voltage gradient measurement device is provided for determining the remaining lifetime of a battery used to power a radio, pager, cellular telephone, or similar device. The battery is attached to a first circuit element to obtain a history of the battery voltage which is used to determine the differential battery voltage. The battery is also attached to a second circuit element which measures the voltage margin between the battery voltage and a reference voltage representing the battery end-of-life condition. A third circuit element divides the voltage margin output of the second circuit element by the differential battery voltage output of the first circuit element to estimate the time that will elapse until the battery voltage approximately equals the reference end-of-life voltage level. This time estimate is used as a basis for performing a variety of functions, including a trigger for a battery shut-off switch to protect radio circuits, and as an activator of indicators to warn the battery user of approaching battery safety thresholds. A method of estimating the remaining useful life of the battery is also disclosed.
66 Citations
20 Claims
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1. A method for determining the time remaining until a battery reaches a first predetermined voltage reference, which represents a first end-of-life voltage, comprising the steps of:
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a) measuring the instantaneous battery voltage at predetermined time intervals to determine a rate of change in the battery voltage; b) measuring the instantaneous battery voltage and comparing the instantaneous battery voltage measurement against the first voltage reference to provide a first voltage margin which is a voltage proportional to the difference between the instantaneous battery voltage measurement and the first voltage reference; and c) dividing the first voltage margin obtained in step b) by the voltage rate of change obtained in step a) to provide a first battery condition, which is a period of time proportional to the time remaining until the instantaneous battery voltage measured in step b) approximately equals the first voltage reference, whereby the remaining useful life of the battery is determined. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A detector for measuring the lifetime remaining until a battery reaches a first predetermined voltage reference which represents a first end-of-life battery voltage, comprising:
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a voltage measuring device selectively connected to the battery for measuring a first battery voltage, which is an instantaneous battery voltage; a first subtractor circuit responsive to said voltage measuring device for measuring the difference between at least two instantaneous battery voltage measurements, made at a predetermined time interval by said voltage measuring device, to provide a voltage change rate which is proportional to the difference between the instantaneous battery voltage measurements; a second subtractor circuit responsive to said voltage measuring device and the first voltage reference, for measuring the difference between the first battery voltage and the first voltage reference, and providing a first voltage margin which is a voltage proportional to the difference between the first battery voltage and the first voltage reference; and a first divider circuit responsive to said first and second subtractor circuits to divide the first voltage margin by the voltage change rate to provide a first battery condition, which is a period of time proportional to the time remaining until the first battery voltage approximately equals the first voltage reference, thereby determining the remaining useful life of the battery. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19)
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20. A detector for measuring the lifetime remaining until a battery reaches a first predetermined voltage reference, which represents a first end-of-life battery voltage, and comprising:
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a first comparator having inputs operatively connected to the battery and the first voltage reference to measure the difference between an instantaneous battery voltage and the first voltage reference, said first comparator providing a first voltage margin which is a voltage proportional to the difference between the instantaneous battery voltage and the first voltage reference; a voltage gradient measuring device operatively connected to the battery and to a clock pulse having a predetermined time interval, to measure the change in the instantaneous battery voltage with respect to an interval of time, said voltage gradient measuring device providing a voltage gradient, which is the battery voltage rate of change; and a first condition analyzer operatively connected to said first comparator and said voltage gradient measuring device for dividing the first voltage margin by the voltage gradient, and to output a first battery condition, which is a period of time proportional to the time remaining until the instantaneous battery voltage approximately equals the first voltage reference, whereby the remaining useful life of the battery is determined.
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Specification