A methodology for calculating the theoretical and practical specific energies of rechargeable batteries, fuels, and materials is presented. The methodology enables comparison of the energy content of diverse systems such as the lithium-ion battery, hydrocarbons, and ammonia. The methodology is relevant for evaluating the possibility of using batteries and renewable fuels in the transportation and grid sectors where fossil fuels are traditionally used as energy sources. It is also relevant for choosing alternatives to petrochemicals for sustainable production of commodity materials. Instructors may consider introducing the proposed methodology in an introductory chemistry class. (Contains 6 tables and 2 figures.)