To be honest - the answer to that question varies... and depend on each individual usage.
For me, it doesn't show any significant battery drainage. Obviously, if you're running any app(s) on your device that is running in the background - it's going to require a little more juice than normal... how many? Not the amount that you might think.. What I would suggest...is to install the app - check to see how much percent of your battery is being used by the app. From your homescreen tap (menu - settings - about phone - phone battery - battery use.) If the battery percent is stationed at any percent (five or lower).. I would consider that OK.(IMO)
There are applications on our phones that uses far more than that.