Thanks. Your reply is very explanatory.
I will implement it in my mainstream thoughts.(I am serious and not trying to be funny.)
But...
OK.... You got me:
Yes, I AM still trying to figure out
my crazy idea.
So imagine two springs. One stronger and one weaker.
If you put the same value weights on both,
stronger will bend less and weaker more which means that
stronger will store less energy and weaker more energy.
So there you have it: energy per kg.
BTW in my language another word for voltage is tension.
(Also I better save this thread right away, because my last thread in this subforum got deleted.)