A practice device for use with a bat in batting sports to instruct a batter on proper swing technique and form. It is a batter assist power trainer for sports exercise. This relates to an exercise method and apparatus for improving performance in sports that include swinging of a device such as a bat. It is a batter assist power trainer device made of an airtight airfoil structure made of flexible and durable material and a method or way for connecting the structure to a bat so that the batter assist power trainer device permits a batter to power train and to controllably increase hitting strength which allows the batter to achieve longer hits of a ball for baseball and/or softball. Other configurations include structures made with end sections, with reinforcing splines; and a various ways to connect the device to the bat.