[@thewizardguy]

The weird thing about darkness is that in this it's like an actual force, as opposed to simply the absence of light. But if the force is removed, "darkness" as a concept wouldn't disappear even if the force itself did. It has to be either matter of some sort or the real definition of darkness, but here it exists as both which makes it difficult. I don't think nothing is by definition darkness in the sense of being used as a power, because that assumes darkness to be an actual thing and therefore not nothing.

But while the act of draining might create darkness if done by light, others would all have to create something for someone else to drain. So I don't think the infinite battery thing is a possibility.