Battery longevity estimator that accounts for episodes of high current drain

System and method for estimating a remaining capacity of a battery of an implantable medical device. The implantable medical device has a battery producing a current and having a remaining battery capacity, the implantable medical device being configured to utilize a relatively low amount of the current and, in specific instances, a relatively large pulse of the current. The processor is coupled to the battery and configured to calculate an estimate of the remaining battery capacity based, at least in part, on a measured battery parameter and occurrences of the specific instances of delivery of the relatively large pulse of the current.