There has been an increased interest in the optimal robot path planning study. However, the optimal path found by the traditional path planning methods only considers distance and time constraints. Thus, it is not necessarily the most energy efficient path. In order to make robots perform more tasks under insufficient energy supply efficiently, reducing energy consumption has become essential in the path planning. In this paper, we proposed a novel path smoothing method that overcomes the deficiencies (e.g., some redundant inflection points in path.) of the traditional A* algorithm. We designed an energy-based adjacency matrix to represent the environmental information in grid map. Then we added a new energy-related criterion based on an adjacency matrix to the cost function of the A* algorithm for path planning. The simulation results demonstrated that the proposed method is more energy efficient than the existing A* algorithm. Moreover, the method realizes a good trade-off between preserving energy and not extending too much the path length. With such advantages, the proposed methods can help indoor wheeled mobile robots or automated guided vehicles (AGVs) to complete path planning tasks with limited power