Anything that comes closer than the event horizon to the black hole is unable to escape from it, as it would need to fly move faster than the speed of light to escape.
This can be seen as the size of the black hole.

The Einstein field equations theoretically describe two radii around a rotating and/or spinning black hole. One of these is the event horizon, beyond which nothing can have an effect to something outside of it. This other one should theoretically lie within a stable black hole. It is currently unclear, what significance (if any) this radius holds.

Around a spinning black hole an effect called "frame dragging" can be observed - objects within an area called it's "ergosphere" are unable to move opposite to the black holes spin, even if they move at the speed of light.
The ergosphere touches the event horizon on the poles, but reaches up to this far out at other angles around the black hole.

For a rotating and/or charged black hole it could theoretically be possible to retrieve energy from it via for example the "Penrose Process". This would (as E=mc^2) decrease the mass of the black hole.
When you extracted enough energy from your black hole to have reached the irreducible mass it will not be possible to retrieve any further energy, thus making this the smallest mass that your black hole could ever be reduced to.

The Penrose process could be able to extract huge amounts of power from a spinning black hole. This would slow the spin of the black hole down until it eventually stops, making it a non-infinite source of energy, but also create enough power within a single second to power the whole world for more than a year.
This is the power your black hole could (in the optimal case) provide and for how long it could keep that up.

The known metrics for black holes only make sense as long as your black holes spin is smaller than or equal to this.

A black hole most likely is not perfectly black, but emits a very slight amount of temperature radiation, known as the "Hawking radiation." This radiation is thought to be a perfect black body radiation. This is the temperature a black body would need to be at to radiate the same amount of energy as your black hole.

If black holes do really radiate energy via Hawking Radiation, a black hole in perfectly "empty" space would slowly radiate away all it's mass until it disappears. Since most black holes as colder than the cosmic microwave background radiation (at 2.7K), this would require the universe to have almost died down already.
This is how long your black hole would still live if everything around it died down.