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An implantable cardiac device, such as a pacemaker, provided with a carbon monofluoride (CF x ) battery. The CF x battery enables replacement of the typical voltage tripler with a voltage doubler and eliminates the need for a bulky decoupling capacitor. The device includes a precision A/D and volt

An implantable cardiac device, such as a pacemaker, provided with a carbon monofluoride (CF x ) battery. The CF x battery enables replacement of the typical voltage tripler with a voltage doubler and eliminates the need for a bulky decoupling capacitor. The device includes a precision A/D and voltage monitor to enable more accurate prediction of impending battery end-of-life. Several methods of accurately determining a pending end-of-life of a battery with a flat voltage output throughout discharge, such as a CF x battery, are provided.

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1. An implantable medical device comprising:a therapy delivery device that is adapted to deliver therapy to an organ of a patient;a controller that controls the delivery of therapy to the organ of the patient;a CF x battery that supplies power to the therapy delivery device wherein the battery has

1. An implantable medical device comprising:a therapy delivery device that is adapted to deliver therapy to an organ of a patient;a controller that controls the delivery of therapy to the organ of the patient;a CF x battery that supplies power to the therapy delivery device wherein the battery has an output characteristic with a substantially non-decreasing output voltage for a first period of time followed by a declining voltage as the battery approaches end-of-life;a battery monitoring circuit, that samples the output voltage of the CF x battery and periodically provides sampled output voltage signals indicative thereof to the controller, wherein the controller determines a predicted end-of-life point of the battery based upon the sampled output voltage signals and wherein the controller monitors the sampled output voltage signals and determines when the sampled voltage signals are indicative of the predictive end-of-life point of the battery. 2. The device of claim 1, wherein the CF x battery has an output voltage characteristic that has an initial beginning-of-life voltage that increases to a peak voltage and then decreases to the predicted end-of-life point. 3. The device of claim 2, wherein the controller determines a peak voltage value from the sampled output voltage signals and then determines a predictive end-of-life point of the battery as occurring when the sampled voltage signals have a magnitude that is a pre-selected magnitude less than the magnitude of the peak voltage value. 4. The device of claim 1, wherein the controller determines a beginning-of-life voltage value based on the sampled voltage output signals and uses the beginning-of-life voltage value to determine the predicted end-of-life point of the battery. 5. The device of claim 4, wherein the controller determines the predicted end-of-life point as the point at which the sampled output voltage signal has a magnitude corresponding to the magnitude of the beginning-of-life voltage value. 6. The device of claim 5, wherein the CF x battery has a beginning-of-life voltage of approximately 2.6 volts and a peak voltage of approximately 2.72 volts. 7. The device of claim 6, wherein the CF x battery provides an output voltage of between approximately 2.6 volts and 2.72 volts for approximately 1700 milliampere hours of operation. 8. The device of claim 1, wherein the battery monitoring circuit comprises:a band gap reference device coupled to the battery that provides a reference voltage that is substantially temperature independent and substantially voltage independent; andan A/D converter that receives the reference voltage and also receives the output voltage from the battery, wherein the A/D converter sends a digital signal to the controller indicative of the ratio between the output voltage from the battery and the reference voltage. 9. The device of claim 8, wherein the A/D converter is a 12 bit A/D converter that provides a digital word to the controller that has a resolution of approximately 1 millivolt. 10. The device of claim 1, wherein the controller periodically receives a plurality of signals from the battery monitoring circuit and wherein the controller normalizes the periodically received values so as to reduce the effect of temporary variations in the output voltage of the battery. 11. The device of claim 10, wherein the controller averages each received sampled output voltage signal with a pre-selected number of previous sampled output voltage values to obtain a periodic value for evaluation of whether the periodic value is indicative of the predictive end-of-life of the battery. 12. The device of claim 11, wherein the battery monitoring circuit provides the sampled output voltage signals on a daily basis. 13. The device of claim 1, wherein the controller sets a flag to indicate that the end-of-life of the battery has been reached such that on subsequent review of the device by a treating medical professional, the treating medical professio nal is advised of the need to replace the battery in the implantable device. 14. The device of claim 1, wherein the therapy delivery device comprises at least one lead adapted to be implanted adjacent the heart of the patient so as to provide electrical stimulation to the heart. 15. The device of claim 1, wherein the controller senses the delivery of therapy by the therapy delivery device and further implements a fuel gauge routine that models battery energy output corresponding to the delivery of therapy and correlates the modeled battery energy output with the sampled voltage signals to determine whether the battery has reached the predicted end-of-life point. 16. An implantable cardiac stimulation device comprising:at least one lead adapted to be implanted adjacent the heart so as to provide therapeutic stimulation to the heart;a therapeutic stimulation circuit that develops electrical stimulation waveforms to be delivered via the at least one lead to the heart;a controller that controls the delivery of therapeutic electrical stimulation to the heart of the patient;a CF x battery that provides power to the implantable cardiac stimulation device wherein the battery has an output characteristic with a substantially non-decreasing output voltage for a first period of time followed by a declining voltage as the battery approaches end-of-life;a battery monitoring circuit that samples the output voltage of the CF x battery and periodically provides sampled output voltage signals indicative thereof to the controller, wherein the controller determines a beginning-of-life voltage value and a predicted end-of-life point of the CF x battery based at least in part upon the beginning-of-life voltage value and wherein the controller monitors the sampled output voltage signals and determines when the sampled voltage signals are indicative of the predictive end-of-life point of the CF x battery. 17. The device of claim 16, wherein the implantable cardiac stimulation device comprises a pacemaker. 18. The device of claim 16, wherein the controller determines a predicted end-of-life point of the CF x battery at a point wherein the output voltage characteristic of the battery is transitioning between a substantially non-decreasing output and a declining voltage. 19. The device of claim 16, wherein the controller determines the beginning-of-life voltage value based on the sampled voltage output signals and uses the beginning-of-life voltage value to determine the predicted end-of-life point of the CF x battery. 20. The device of claim 19, wherein the controller determines the predicted end-of-life point as the point at which the sampled output voltage signals have a magnitude corresponding to the magnitude of the beginning-of-life voltage value. 21. The device of claim 20, wherein the CF x battery has a beginning-of-life voltage of approximately 2.6 volts and a peak voltage of approximately 2.72 volts. 22. The device of claim 21, wherein the CF x battery provides an output voltage of between approximately 2.6 volts and 2.72 volts for approximately 1700 milliampere hours of operation. 23. The device of claim 16, wherein the controller determines a peak voltage value from the sampled output voltage signals and then determines a predicted end-of-life point of the CF x battery as occurring when the sampled voltage signals have a magnitude that is a pre-selected magnitude less than the magnitude of the peak voltage value. 24. The device of claim 16, wherein the battery monitoring circuit comprises:a band gap reference device coupled to the battery that provides a reference voltage that is substantially temperature independent and substantially voltage independent; andan A/D converter that receives the reference voltage and also receives the output voltage from the battery, wherein the A/D converter sends a digital signal to the controller indicative of the difference between the output voltage from the battery and the reference voltage. 25. The device of claim 24, wherein the A/D converter is a 12 bit A/D converter that provides a digital word to the controller that has a resolution of approximately 1 millivolt. 26. The device of claim 16, wherein the controller periodically receives a plurality of signals from the battery monitoring circuit and wherein the controller normalizes the periodically received values so as to reduce the effect of temporary variations in the output voltage of the CF x battery. 27. An implantable cardiac stimulation device comprising:means for delivering therapy to the heart of a patient;means for controlling the delivery of therapy to the heart of the patient;means for supplying power to the implantable cardiac stimulation device wherein the means provides a relatively non-decreasing output voltage over a normal useful life and then transitions into an end-of-life state wherein the output voltage declines from the relatively non-decreasing output voltage;means for monitoring the output characteristics of the battery, wherein the monitoring means periodically samples an output characteristic of the battery and provides an output signal indicative thereof, wherein the means for controlling receives the output signals and uses the output signals to (i) determine a predicted end-of-life point of the means for supplying power based on a beginning-of-life voltage value and (ii) determining whether the output signals are indicative of the means for supplying power having reached the predicted end-of-life point based on the beginning-of-life voltage value. 28. The device of claim 27, wherein the means for supplying power comprises a CF x battery. 29. The device of claim 28, wherein the effective series resistance of the battery at beginning-of-life and at the end-of-life is an order of magnitude less than the effective series resistance of an equivalent Li battery used in implantable cardiac stimulation devices. 30. The device of claim 28, wherein the control means determines a predicted end-of-life point of the battery by determining a beginning-of-life voltage for the battery and determining that the predicted end-of-life point of the battery will occur when the output signals from the battery monitoring means indicate that the voltage of the battery corresponds to the beginning-of-life voltage. 31. The device of claim 28, wherein the control means determines a predicted end-of-life point of the battery by determining a peak voltage of the battery based on the output signals provided by the battery monitoring means and then determining that the predicted end-of-life point of the battery will occur when the output signals from the battery monitoring means indicate that the voltage of the battery has a magnitude that is a pre-selected amount less than the peak voltage. 32. The device of claim 28, having telemetry of greater than 10 kbaud. 33. The device of claim 27, wherein the delivery means comprises a pacing lead. 34. The device of claim 27, wherein the delivery means comprises a defibrillation coil. 35. The device of claim 27, wherein the monitoring means comprises:a band gap reference device coupled to the battery that provides a reference voltage that is substantially temperature independent and substantially voltage independent; andan A/D converter that receives the reference voltage and also receives the output voltage from the battery, wherein the A/D converter sends a digital signal to the control means indicative of the difference between the output voltage from the battery and the reference voltage. 36. The device of claim 27, wherein the control means develops a normalized battery voltage signal corresponding to each of the output signals wherein the normalized battery voltage signal is processed so as to reduce the effect of temporary variations in the output voltage in the means for supplying power. 37. The device of claim 36, wherein the control means averages each receives sampled output signals with a pre-selected number o f previous sampled output signals to obtain a periodic value for evaluation of whether the periodic value is indicative of the predicted end-of-life of the means for supplying power. 38. The device of claim 27, wherein the therapy is antitachycardia pacing.