Publisher Summary This chapter deals with the discussion of guidelines to battery selection. The first choice to be made is whether a primary or secondary battery is required. There is increasing environmental pressure to stop the use of mercury batteries. As these are still used to a limited extent. Previously primary batteries were zinc-anode-based systems. Performance of these cells has undergone progressive improvements through development of the original Leclanché (carbon-zinc) system and introduction of new couples such as zinc-mercuric oxide, alkaline manganese dioxide, and zinc-silver oxide. There are three basic applications for which primary batteries are used: miniature equipment; equipment that is portable in use; transportable equipment, and standby systems. On the other hand, secondary batteries are the rechargeable batteries. Five major types of secondary rechargeable batteries discussed are lead-acid, nickel-cadmium, silver-zinc, silver-cadmium, and nickel-zinc. Determining the battery requirements includes: physical- size and weight limitations, shape, shock and vibration resistance use; electrical- voltage, current drain, constant, discharge schedule; environmental - storage and operating temperatures; special considerations- cost, replace, service life, shelf life, operating schedule, activation.