I have yet to have the batteries die in any of my Aimpoints, and I leave them on, 24/7/365. They get changed once a year.
You should absolutely know how to use iron sights, and if the gun is capable, should have a set of BUIS on it, but the red dots absolutely do blow the irons out of the water for most realistic shooting.
Zeitgeist - The movie
Zeitgeist - Addendum