Can You Have a 100% Dark Chocolate Bar?

It's almost certainly the case that every black hole contains some dark matter. While a big cloud is hard to collapse into a black hole, if you have an existing black hole in the dark matter particle just like heads towards it, it's just going to fall in. The no hair theorem tells us we can know the mass of the black hole, basically how much stuff is in it. You can measure its charge increasing or decreasing as you add charge to it because charges conserved in our universe.