Patent ID: 7580749

Claim:
A system, including: a battery power terminal for a battery; sensing and pacing control circuitry electrically connected to the battery power terminal; a pacing supply storage (PSS) capacitor electrically connected to the battery power terminal and to a discharge switch; comparison circuitry, including: a first comparator electrically connected to the battery power terminal and adapted for comparing a battery terminal voltage (Vbatt) to a brownout voltage (Vstop), the first comparator having a first comparator output; a second comparator electrically connected to the PSS capacitor and adapted for comparing a pacing supply storage voltage (Vcs) to at least one reference voltage (Vx), the second comparator having a second comparator output, wherein the first comparator output and the second comparator output are adapted to control current flow from the battery power terminal to the PSS capacitor; and charge time measurement (CTM) control circuitry electrically connected to the sensing and pacing control circuitry, the comparator circuitry and the discharge switch, the charge time measurement control circuitry being adapted to: access a predetermined set of charge time measurement set-up parameters and a predetermined elective replacement time (ERT) charge time limit determined from a battery resistance ERT target that corresponds to a charge depletion target; determine a rate of charge storage in the PSS capacitor using the predetermined set of charge time measurement set-up parameters; compare the determined rate of charge storage in the PSS capacitor to the predetermined ERT charge time limit for the predetermined set of charge time measurement set-up parameters; and declare an ERT based on a number of comparisons between the determined rate of charge storage in the charge storage capacitor and the ERT charge time limit.