Patent ID: 8560070

Claim:
An implantable medical device comprising: an energy storage device; a stimulation unit that is operatively coupled to the energy storage device and configured to provide an electrical signal; a memory device configured to store first electrical charge depletion rate information associated with an idle mode and second electrical charge depletion rate information associated with a stimulation mode; and a controller that is operatively coupled to the memory device, the stimulation unit and the energy storage device, wherein the controller comprises: a charge depletion determination unit configured to estimate an amount of energy depleted during operation based on a first depletion amount and a second depletion amount, wherein the first depletion amount is calculated based on the first electrical charge depletion rate information applied to one or more periods associated with the idle mode, and wherein the second depletion amount is calculated based on the second electrical charge depletion rate applied to one or more periods associated with the stimulation mode; a voltage determination unit configured to determine whether a measured voltage across the energy storage device is greater than or equal to a transition voltage of the energy storage device; and an energy indicator unit configured to indicate an amount of energy remaining in the energy storage device, wherein when the measured voltage is greater than or equal to the transition voltage, the amount of energy remaining is determined based on the amount of energy depleted, and wherein when the measured voltage is less than the transition voltage, the amount of energy remaining is determined based on a difference between the measured voltage and a voltage associated with end of service of the energy storage device.