So is this weapon supposed to drain the all power from the planet merely by existing, or does it drain it only once it is fired upon the enemy fleet?

The latter is what I understood to be the case and would make the most sense, but dialogue with Carsiri and Madine suggests that Balmorra will pay that price no matter what, even if the Republic would simply possess it as a deterrent against future Empire invasions.

Can anyone shed some light on this?