I know there are a lot of people when they need ripe, mashed bananas for a recipe just throw them in with the mix whole and let their beater do the "mashing." I used to be one of those people, but let me tell you there is a difference between mashing them and then putting them in the mix compared to just letting your mixer do the "mashing."
All you want to do is peel your bananas - put on a dinner plate, cutting board, etc and then use a fork to mash. Because the bananas will already be pretty ripe, you'll really only need to go over them once with the fork. Easy peasy and believe me, you'll notice a difference in your batter! :)