I had Panasonic cordless phones with a similar supercap that was used to store data like number lists and such in them Those caps never did that, the only failures were the leads breaking off and the cap rattling around loose in the case. 0.022F 5V cap with through hole leads. I retired the last one ( mine) last year as I had run out of spare parts for it, it did 15 years of work. I had a pile that I used for RF modules, antenna's, microphones, speakers, cases and keypad rubbers. The handset flap latches were weak, so I modified it to use a small magnet ( CDROM lens motor) and a reed switch to replace the switch as well. These were expensive units, costing around $150 each when new.