meyerweb#CB
Banned
Unlike widgets, I don't think the cards are active until you open Google search. So they shouldn't pull any extra power unless you have them visible all of the time.
No, at least some cards update in the background. If you click on the menu buttons you'll see an option for turning background updates on or off, and to set the priority. And GNow has to be running in the background to know when to create a new card based on where you are. That said, I haven't noticed much of a battery hit.