The full-automatic replacing batteries robot instead of human, can automatically replace the batteries in the Electric Vehicles (EV). The positioning system, which solves the problem of the battery localization due to the EV's random position, is the key of replacing the batteries successfully for a full-automatic robot. The positioning system utilizes monocular camera to get the pose information of batteries, and achieves the goal of accurate positioning for the batteries. In this paper, we introduce the design proposal, constitution and working procedures of vision location system of the full-automatic replacing batteries robot. Experimental results validate that our proposed system works with high accuracy, robustness and safety.