From what I've seen of the 8703 it has a pretty solid battery. The app will sit in the background and since it's event driven should take up very little cpu usage. When it is in notification mode I would imagine it would use up more juice though... I don't think it would use much power compared to the radio or backlight but I'm not sure exactly how much it uses when in notification mode.

So I would imagine there would be some battery drain but not sure if it would be noticeable or not.