This recommended practice describes a method for sizing both vented and valve-regulated lead-acid batteries in stand-alone PV systems. Installation@ maintenance@ safety@ testing procedures@ and consideration of battery types other than lead-acid are beyond the scope of this recommended practice. Sizing batteries for hybrid and grid-connected PV systems is beyond the scope of this recommended practice. Recommended practices for the remainder of the electrical systems associated with stand alone PV installations are also beyond the scope of this recommended practice Sizing examples are given for various representative system applications. Iterative techniques to optimize battery costs@ which include consideration of the interrelationship between battery size@ PV array size@ and weather@ are beyond the scope of this recommended practice. Purpose This recommended practice is meant to assist system designers in sizing lead-acid batteries for residential@ commercial@ and industrial stand-alone `PV systems.