First find out what they have and if you can. I don’t know what their defenses are so I can’t tell you.
You basically need to be better at energy working than them and be able to drain faster than they can replenish.
And if you don’t like something about them, and you just take their energy, be aware you can take on those traits that caused you to not like them, as you will slightly become them… you are what you eat. If they are sick you can also take on that overt imbalance and get sick too. To address this there’s a concept called "filtering’, but I think it’s risky nevertheless. Personally I would drain the energy into the ground.
Try the book here to figure out what kinds of defense are available so you can scan for them.