Sounds like a supercapacitor. They have been a dream for decades to replace car/laptop batteries. Simple and quick high (read not readily available) charging in minutes for vehicles seconds for less energy intensive items.
https://en.wikipedia.org/wiki/Supercapacitor
DK
Ah, a flux capacitor! But can you get 1.2 Gigawatts and fit it into a DeLorean?