I got two 2.7V 100F supercapacitors. I have wired them in series and applied 5V.
One capacitor I have tried have been about 2V. I put it on my desk without any connection.
A couple of hours later, when I measured the voltage of capacitor, it was about 0.5V.
So, energy formula of a capacitor says that it is proportional with 2nd power of capacitor voltage. In my case, voltage dropped 4 times and rate of energy loss is about 16 times.
I cannot figure out where this energy has gone.