This Recommended Practice describes a method for sizing both vented and valve-regulated lead-acid batteries used with photovoltaic (PV) systems. Installation, maintenance, safety, testing procedures, and considerations of battery types other than lead-acid, are beyond the scope of this document. Recommended practices for the remainder of the electrical systems associated with PV installations are also beyond the scope of this document. 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 document. This recommended practice is meant to assist system signers in sizing lead-acid batteries for residential, commercial, and industrial PV systems. Revision Standard - Superseded. A method for sizing both vented and valve-regulated lead-acid batteries used in terrestrial photovoltaic (PV)systems is described. Installation,maintenance,safety,testing procedures,and consideration of battery types other than lead-acid are beyond the scope of this document. Recommended practices for the remainder of the electrical systems associated with PV installations are also beyond the scope of this document.