I have compared the leakage current of a few Lithium Ion Capacitors (LIC) to a few supercapacitors (EDLC). I charged them up and then almost every day I measured the voltage decay with a handheld  multimeter and calculated leakage current using following formula
leakagecurrent(A)=capacity(Farad)*(yesterdaysvoltage[V]-todaysvoltage[V])/t[s]

The chart shows for both LICs and EDLCs that after 72 hours the leakage current is less than 5uA, which is good news for low power IoT devices. Interestingly the high capacity (>200F) LICs have a lower leakage than the 10F supercapacitors. And if you plot the leakage per Farad capacity, then it becomes even more clear that LICs have about 5 times lower leakage than supercapacitors.