[@Kiyran]
Darkness is the absence of light, and therefore in order to 'remove' darkness from a room you would need to introduce light. Nothingness by definition is dark, because it lacks light. This is why defining darkness as a 'force' is so difficult, because it's an absence.

Although I personally kind of like the idea of opposites being able to charge each other up. And they'd still only be able to charge up to the upper limit of the power stones, so it's not like this would suddenly grant them godlike powers.

But yeah, it depends on how those powers are going to work. Even without the idea of an infinite-power-battery I'm interested in what happens when a Darkness user drains power from darkness.