Originally Posted by Ma ping
"Force vampires" do not gain Force enrgy during a battle, they gain it once their opponent is defeated. They don't siphon it while they're fighting.
A Force Vampire (both light and dark) can use the Force Drain ability more effectively than other Force users, simply because it comes naturally to them. The Exile could drain Anakin of his powers and life before he took two steps. Just look at the way Kreia used it on the Jedi Masters. She wasn't even a Force Vampire, and she killed them all and made them devoid of the Force without even trying. Imagine what the Exile could do if she really tried...