BPs do not need a lot of food. Some only eat a few times per year and are still completely healthy. Others eat every week and are completely healthy. Feed your snake whatever it perfers and then you will both be happy. If you are going to feed him Rats I would recommend stunning or prekilling. Mice on the other hand, don't really need to be stunned or prekilled IMO, since they can't do much damage anyway. If you can get you snake to eat prekilled, don't ever feed anything else, prekilled is safer and a lot of the time cheaper if you have access to bulk frozen prey.
Usually, I can tell when my snakes are hungry. When I walk into the room, instead of recoiling into his hide, he will pick his head up a little and assume strike position...then I now its time to feed him. Also, they can be more restless, moving about the cage at night when they are hungry.