If you are of the former probably heard that 1F capacitors (farads) are the size of a room. No more! Now there are more tiny capacitors, that may one day replace batteries in many applications. These below are 6cm in height and have 500F/2.7 V.
The only problem is the low voltage, that prevents use in various applications. One day this problem can be solved. I bought two capacitors thinking about putting them in series reaching more than 5V.
One of the capacitors came with additional terminals, probably for higher input current load.
Look at the size of them in the photo below:
My preliminary tests showed that the capacitor discharges very quickly, about of 3%, even without load. Are still lower than the lithium batteries. But are the beginning of a technology that could work. I leave the link to the product, for those who want to test: