Hello.
In several of my projects I'm using 5.5V 0.47F supercaps made by Eaton, to back-up DS3231 RTC.
Supercaps are charged via 1N4148 and 330 ohm resistor from 5 volts.
I have several devices, which were made 2-3 years ago, and when they were fresh, supercap charge was enough for 3-4 days of standby. Now it is about 2-3 hours. The total full discharge/charge cycle for these 2-3 years would not exceed 10-15 times, temperature was always below 40C.
So it is normal them to loose capacity that much, considering non-existent abuse?