A method and an apparatus for projecting an end of service (EOS) and/or an elective replacement indication (ERI) of a component in an implantable device is provided. The method comprises measuring the measured voltage of the energy storage device, and determining whether the measured voltage is less than a transition voltage. When the measured voltage is less than the transition voltage, determining a time period remaining until an end of service of the energy storage device is based upon a function of the measured voltage. When the measured voltage is greater than or equal to the transition voltage, determining a time period remaining until an end of service of the energy storage device is based upon a function of the total charge depleted. The transition voltage is a voltage associated with the transition point of non-linearity in the battery voltage depletion curve.