Unless there is battery technology that they are withholding, they can only fit so many electrons in batteries.
It still is an issue, even with batteries.
How big is an electron? How big is an atom? Lots and lots of electrons available.. certainly there is a limit.. its a calculation that involves Coulombs law and Avogadro constant and the specific density of the material proposed.
But, I am not interested in doing that at this moment.