One of less well known facts about black holes is that they are best known method to convert mass into energy. Black hole can be used to recover up to 40% of falling mass as energy.
Also, technically, Hawking radiation is not the only way to get the energy out of black hole. You can extract energy from a rotating black hole. Normally, rotational energy contributes to the total mass of the black hole, but you can extract that energy, robbing black hole of some of its rotational energy and consequently, reducing its total mass. Essentially, it can be used to accelerate objects (this is called Penrose process).
When two black holes collide, a portion of their mass is radiated as gravitational waves. This has been verified by LIGO showing that the resulting black hole has less mass than the sum of mass of black holes before collision.
I am also pretty sure that a charged black hole could act as a fantastic battery, except there is no known mechanism that could create a significantly charged one.