Don't kill the bats, you have openings in the attic that they are coming in & out. Those openings need to be sealed. There is something on the market called a Riddex plug in the wall. It keeps critters out. Bats have a lot of droppings. They go out when it starts to get dark and come back before it gets light. If you don't have an easy access to your attic you might need to get a professional to help you. Bats eat many times their weight in bugs that fly in the night time. You just don't need them in your home. If you are able to get up there wear a mask. We have 6 bats that come out of a hole in a tree every evening and fly around eating & diving for bugs. We sit & watch them.