Method for monitoring end of life for battery

• US 6,631,293 B2
• Filed: 04/23/2001
• Issued: 10/07/2003
• Est. Priority Date: 09/15/1997
• Status: Expired due to Fees

• Current Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Original Assignee: Cardiac Pacemakers Incorporated (Boston Scientific Corporation)
• Inventors: Lyden, Michael J.
• Primary Examiner(s): Evanisko, George R.
• Assistant Examiner(s): KHAN, OMAR A
• Application Number:
  US09/840,408
• Publication Number:
  US 20010034541A1
• Time in Patent Office: 897 Days
• Field of Search: 607/29
• US Class Current: 607/29
• CPC Class Codes: A61N 1/3708 for power depletion
• CPC Class Codes: G01R 31/3647 for determining the ability of a battery to perform a critical function, e.g. cranking
• CPC Class Codes: G01R 31/367 Software therefor, e.g. for battery testing using modelling or look-up tables
• CPC Class Codes: G01R 31/392 Determining battery ageing or deterioration, e.g. state of health
• CPC Class Codes: H02J 2310/23 The load being a medical device, a medical implant, or a life supporting device
• CPC Class Codes: H02J 7/0048 Detection of remaining charge capacity or state of charge [SOC]
• CPC Class Codes: H02J 7/005 Detection of state of health [SOH]

Abstract

A system is described which has a battery, a device which is powered by the battery in an episodic manner, and a charge storage capacitor. The system has attached to the charge storage capacitor a device or devices capable of: reading the rate of charge storage; or measuring both time and charge stored or added to the charge storage capacitor so that a rate of charge storage may be calculated. The estimated replacement time for the battery, particularly for a lithium battery in a pacing device, is easily estimated. Also described herein is a process for estimating a level of energy depletion in the system. The process comprises: finding a relatively quiescent period in powering of the device in the episodic manner; determining a rate of charging in the storage capacitor during the quiescent period; and correlating the rate of charging in the storage capacitor to a value of internal impedance in the battery through a comparison with known relationships for the battery and rate of charging to determine a value for the internal impedance of the battery.

Claims

1. A process for estimating a level of power depletion in a system having a lithium battery, a cardiac pacing device powered by said lithium battery in an episodic manner, and a charge storage capacitor, said system having attached to said charge storage capacitor a device or devices capable of:

reading the rate of charge storage;

or

measuring both time and charge stored or added to said charge storage capacitor and calculating a rate of charge storage, said process comprising;

finding a relatively quiescent period in powering of said cardiac pacing device in said episodic manner;

determining a rate of charging in said storage capacitor during said quiescent period, including determining said rate of charging over a time period beginning when the capacitor is not fully discharged and has a predetermined minimum charge differential across the capacitor so that the storage capacitor is discharged to at least said predetermined minimum upon initiation of an episodic charging event; and

determining a value for an internal impedance of said battery using known relationships with respect to said rate of charging for said battery.

2. The process of claim 1 wherein determining a value for an internal impedance of said battery includes using a look-up table having predetermined quantitative comparisons of measured capacitor charge rates and internal impedance for a particular battery.

3. The process of claim 1 wherein after determining a value for an internal impedance of said battery, determining a value for expended energy from said battery using said internal impedance value.

4. The process of claim 3 further comprising effecting an ERT flag for a predetermined amount of expended energy.

5. The process of claim 4 wherein effecting an ERT flag includes creating said ERT flag.

6. The process of claim 5 further comprising transmitting said ERT flag to a programmer.

7. The process of claim 3 wherein determining a value for expended energy from said battery using said internal impedance value includes referencing a graphic representation of a relationship between internal impedance of said battery and energy expended from said battery.

8. The process of claim 7 wherein said quiescent period immediately follows an atrial pace or atrial pulse.

9. The process of claim 7 wherein said quiescent period immediately follows a ventricular pace or pulse.

10. The process of claim 3 wherein said quiescent period immediately follows an atrial pace or atrial pulse.

11. The process of claim 3 wherein said quiescent period immediately follows a ventricular pace or pulse.

12. The process of claim 1 further comprising energizing a pace from said pacing system to a patient using energy stored in said storage capacitor.

13. The process of claim 1 wherein said quiescent period immediately follows an atrial pace or atrial pulse.

14. The process of claim 1 wherein said quiescent period immediately follows a ventricular pace or pulse.

15. The process of claim 1 further comprising comparing said value for the internal impedance of said battery to known relationships between the internal impedance of the battery and energy depletion from said battery.

16. A process for estimating a level of energy depletion in a system having a battery, a device powered by said battery in an episodic manner, and a charge storage capacitor, said system having attached to said charge storage capacitor a device or devices capable of:

reading the rate of charge storage;

or

measuring both time and charge stored or added to said charge storage capacitor and calculating a rate of charge storage, said process comprising;

finding a relatively quiescent period in powering of said device in said episodic manner;

determining a rate of charging in said storage capacitor during said quiescent period, including determining said rate of charging over a time period beginning when the capacitor is not fully discharged and has a predetermined minimum charge differential across the capacitor so that the storage capacitor is discharged to at least said predetermined minimum upon initiation of an episodic charging event; and

correlating said rate of charging in said storage capacitor to a value of internal resistance in said battery through a comparison with known relationships for said battery and rate of charging and determining a value for the internal resistance of said battery.

17. The process of claim 16 wherein said battery comprises a battery characterized by having an internal impedance characteristic curve which is initially substantially linear as a function of energy depletion, but which asymptotically approaches an energy production limit and increasing internal impedance.

18. The process of claim 17 wherein said battery comprises a lithium battery.

19. A process for estimating a level of power depletion in a cardiac pacing system having a lithium battery, a first cardiac pacing device electrically connected to said lithium battery and a charge storage capacitor electrically connected to said lithium battery, said first cardiac pacing device operating in an episodic matter and powered by said lithium battery, said cardiac pacing system having at least one second device attached to said charge storage capacitor, and the second device:

reads a rate of charge storage within said storage capacitor without disconnecting the electrical connection between said charge storage capacitor and said lithium battery;

or

measures both charge added to said charge storage capacitor and a time when said charge is added to said charge storage capacitor, said measuring of both charge added to said charge storage capacitor and a time when said charge is added to said charge storage capacitor being performed without disconnecting the electrical connection between said charge storage capacitor and said lithium battery, and calculating a rate of charge storage in said charge storage capacitor,

said process comprising the steps of adding charge to said charge storage capacitor from said lithium battery and;

finding a relatively quiescent period in of said first device in said episodic manner;

determining a rate of said charge storage in said charge storage capacitor during said relatively quiescent period, including determining said rate of charging over a time period beginning when the capacitor is not fully discharged and has a predetermined minimum charge differential across the capacitor so that the storage capacitor is discharged to at least said predetermined minimum upon initiation of an episodic charging event; and

correlating said rate of charging in said charge storage capacitor to a value of internal resistance in said lithium battery to determine a value for the internal impedance of said lithium battery,

said internal impedance being used to estimate a level of energy depletion in the cardiac pacing system having said lithium battery.

20. The process of claim 19 wherein said internal resistance is an internal AC impedance, and after determining a value for internal AC impedance of said lithium battery, determining a value for expended energy from said lithium battery using said value for internal AC impedance of said lithium battery.

21. The process of claim 20 wherein after determining said value for internal AC impedance of said lithium battery, determining a value for expended energy using said determined value and referencing a graphic representation of a relationship between internal AC impedance of said lithium battery and energy expended from said lithium battery.

22. The process of claim 21 further comprising an atrial pulse or atrial pace to a patient from said charge storage capacitor, wherein said quiescent period immediately follows an atrial pace or atrial pulse.

23. The process of claim 21 further comprising providing a ventricle pulse or ventricle pace to a patient from said charge storage capacitor, wherein said quiescent period immediately follows a ventricular pace or ventricular pulse.

24. The process of claim 20 further comprising providing a ventricle pulse or ventricle pace to a patient from said charge storage capacitor, wherein said quiescent period immediately follows a ventricular pace or ventricular pulse.

25. The process of claim 20 further comprising providing an atrial pulse or atrial pace to a patient from said charge storage capacitor, wherein said quiescent period immediately follows an atrial pace or atrial pulse.

26. The process of claim 19 further comprising signaling that an estimated replacement time has been approached using an estimated replacement time (ERT) flag when reaching a stage of a predetermined amount of expended energy.

27. The process of claim 26 further comprising, after said second device measures a charge time, said second device activating said ERT flag using a predetermined charge time.

28. The process of claim 27 further comprising said second device transmitting said ERT flag to a programmer.

29. The process of claim 19 wherein said lithium battery has an internal impedance, and said determining a rate of said charge storage includes using a look-up table having predetermined quantitative comparisons of measured capacitor charge rates for said charge storage capacitor and internal impedance for said lithium batttery.

30. The process of claim 19 wherein said storage capacitor is used to store energy and said stored energy is used to energize a pace from said cardiac pacing system to a patient, and a pace is provided to said patient with energy stored in said charge storage capacitor.

31. The process of claim 19 further comprising providing an atrial pace or atrial pulse to a patient from said charge storage capacitor, wherein said quiescent period immediately follows said atrial pace or atrial pulse.

32. The process of claim 19 further comprising providing a ventricle pulse or ventricle pace to a patient from said charge storage capacitor, wherein said quiescent period immediately follows said ventricular pace or ventricular pulse.

33. The process of claim 19 further comprising comparing said value for the internal impedance of said battery to known relationships between the internal impedance of the battery and energy depletion from said battery.

34. A process for estimating a level of energy depletion in a battery in a system having a lithium battery, a first device operating in an episodic manner electrically connected to and powered by said lithium battery, and a charge storage capacitor electrically connected to said lithium battery, said system having at least one second device attached to said charge storage capacitor to determine a rate of charging of said charge storage capacitor, and the process comprising said at least one second device:

reading the rate of charging of said charge storage capacitor;

or

measuring both charge added to said charge storage capacitor and a time when said charge is added to said charge storage capacitor, said measuring of both charge added to said charge storage capacitor and a time when said charge is added to said charge storage capacitor being performed without disconnecting the electrical connection between said charge storage capacitor and said lithium battery, and calculating said rate of charging,

said process further comprising the steps of adding charge to said charge storage capacitor from said lithium battery and;

finding a relatively quiescent period in powering of said first device in said episodic manner;

determining said rate of charging in said charge storage capacitor during said relatively quiescent period including determining said rate of charging over a time period beginning when the capacitor is not fully discharged and has a predetermined minimum charge differential across the capacitor so that the storage capacitor is discharged to at least said predetermined minimum upon initiation of an episodic charging event;

correlating said rate of charging in said charge storage capacitor to a value of internal impedance in said lithium battery to determine a value for internal impedance of said battery; and

comparing said value for internal impedance of said lithium battery with known relationships between said internal impedance of said lithium battery and depleted charge from said lithium battery to estimate the level of depletion of said lithium battery.

35. The process of claim 34 wherein said battery comprises a battery having an internal resistance characteristic curve, wherein the curve is initially substantially linear as a function of energy depletion, but wherein the curve asymptotically approaches an energy production limit and increasing internal resistance.

36. The process of claim 35 wherein said battery comprises a lithium battery.