Before you go to the mall, make sure you go to buy mode and activate the cheatcodes' box. Press Ctrl+Alt+C. (Don't put in the pluses!) Then, type move_objects on. After that, use your mouse to click on the sim you want to give full energy to. Delete that sim by pressing the delete button. Go back to live mode. You will see that your sim has disappeared. Click on the sim's face in the face gallery. Your sim will then reappear! Call the cab to take you sim to downtown. When your sim's mood bars starts to glow red, call a cab to go back home, delete the sim again, make him or her reappear again then call the cab to take your sim back to downtown!