2. Introduce cellular energy and ATP (adenosine triphosphate [tri = three]) by displaying some rechargeable batteries and discussing with students what rechargeable batteries do and how they work. Describe an analogy between ATP and the batteries: As the batteries are used, they give up their potential energy until all of it has been converted into kinetic energy and heat/unusable energy. Spent rechargeable batteries can be used again only after input of additional energy.