The “holy grail”: a lightweight ultracapacitor, a few cubic feet in size, able to run an electric car several hundred miles and recharge in a few minutes.
One problem with ultracapacitors: propensity to instant discharge if possible. Safety is a huge issue when capable of dumping 100kW/h thru someone in a millisecond.
That's getting the short end of the stick. Resistance would be futile.
And yes, I've got no shortage of horrible puns. I should be grounded for it.
It is Friday afternoon, after all.