So one thing to weigh in on here if you haven't figured out from comments and chat is that the science behind blackholes let alone their existance is all theorical. As of just recently man kind has finally photographed such an event, which only proves their existence, but still sheds not light (pun intended) on their construction or how they work.
That said, there is no shortage of theoretical data and hard evidence about these objects. Astrophysicist have detailed for example how light behaves in black holes and how that's persevered, and the late Steven Hawking discussed a concept of Hawking Radiation which is a type of radiation he postulated "burned off" or evaporated from a black hole. This in could be your crutch to explain your question above. Perhaps harnessing this massive electrical output into a system or process that retained that radiation to the event horizon, or controlled it's evaporation/build up. Perhaps with enough exposition you could write your own way of claiming this "fringe science" keeps the hole open.
TL:DR; Look up Hawking Radiation as a possible help and make up the rest, since black holes are as close to science fiction real life can get. https://en.wikipedia.org/wiki/Hawking_radiation