How can I tell which tweaks use battery?

[Barty]

I have a few tweaks installed. I think some tweaks only modify a plist somewhere while others like activator are probably running in the background and using up battery.

How can I tell for sure which is which?

For example, how much battery does f.lux use?

I want to install a theme and change some of the ugly icons in ios 7. Does winter board runs constantly in the background to modify the UI? Or is it a one time application?

Thanks.