The greatest breakthrough in physics in the history of humanity was made, by utter accident, by Dr Robert Lilis while working on ways to wirelessly broadcast power. It had been known for more than a century that it was possible to create a singularity by colliding enough radiation energy into a single point, but what he discovered by accident was that if the radiation came from 7 equally spaced points, it would impart that energy in such a way that caused the newborn singularity to be spinning when it was created, a ringularity.
This is important because while a small singularity can be useful for some purposes (See Singularity Drive), a spinning ringularity has some other, far more interesting users. It can serve as a battery, storing that rotational energy and giving it back on demand as we slow that spin.
How this works is that a ringularity generates enough gravity, mass, and energy that it warps space-time around it, dragging it with it as it spins into a region of space-time known as the ergosphere, a region of space-time that is moving along with the blackhole. For an artificial ringularity that the one Dr Lilis discovered how to make, this region is only a few feet across… but if you put gamma-radiation mirrors around it, and shoot in gamma radiation, something odd and very cool happens called hyper-radiant scattering, where the black hole’s spin slows a little, and some of the gamma radiation is sucked into the blackhole, and what is left becomes far, far more energetic and can be gathered up to produce more energy that was put in, basically using the blackhole’s spinning motion as a giant battery.
The effect of this is that the HEF can, on short notice, generate incredible amounts of energy… like when they are passing through a wormhole to keep their momentum intact and escape the tunnel before the tunnel collapses back to a singularity again. Without a device such a thing, traveling through a wormhole is probably impossible.
As a side benefit, this region of space-time generates gravity, so by placing the drive on the bottom deck of the ship, humanity creates artificial gravity for their spaceships.