Publisher Summary This chapter briefly discusses secondary batteries. A classical method of representing a discharge curve for a secondary battery is to plot terminal voltage against time into the discharge at a stipulated battery temperature and constant current discharge rate. Such curves can be prepared at several different battery temperatures in order to establish the effect of temperature on the voltage-time relationship. The voltage characteristics for a cell can be portrayed as a plot of terminal voltage versus discharge time at a stipulated discharge rate and battery temperature. A useful method of studying the effect of temperature on the performance of lead-acid, silver-cadmium and silver-zinc batteries is to plot plateau voltage obtained at various rates of discharge against battery temperature at stipulated rates of discharge. Further, capacity returned-discharge current curves, discharge rate-capacity returned curves, discharge rate-terminal voltage curves, discharge rate-mid-point voltage curves, and discharge rate-energy density curves followed by self-discharge characteristics, float life characteristics.