Patent ID: 7515962

Claim:
A pacemaker, including: a battery power terminal for a pacemaker battery; a capacitor electrically connected to the battery power terminal; pacemaker control circuitry electrically connected to the battery power terminal and the capacitor for controlling current flow from the battery power terminal to the capacitor to charge the capacitor and to discharge the capacitor to a discharge voltage level (Vd) before beginning a time charge measurement; and charge time measurement (CTM) control circuitry electrically connected to the pacemaker control circuitry and adapted to: access a predetermined set of charge time measurement set-up parameters and a predetermined elective replacement time (ERT) charge time limit associated with an AC impedance target for the battery; determine a rate of charge storage in the capacitor using the predetermined set of charge time measurement set-up parameters; and declare an ERT using the determined rate of charge storage in the capacitor and the ERT charge time limit, wherein the predetermined set of charge time measurement set-up parameters to be accessed by the CTM control circuitry include: a final capacitor voltage (VF) to end the charge time measurement for determining the rate of charge storage in the capacitor; and an initial capacitor reference voltage (VI) to begin the charge time measurement for determining the rate of charge storage in the capacitor, VI being greater than Vd.