App note from KEMET about supercapacitor’s leakage and self discharge and their differences in order to take account the back-up time of an application. Link here (PDF)
Supercapacitor is widely used for RTC backup application to provide power to RTC circuit in electronics when the power source to the system is disconnected. Self-discharge characteristics is one of the important characteristics to determine the backup time. Self-discharge current is often confused with leakage current characteristic.