The storage battery is of primary importance in ensuring the satisfactory operation of generating stations@ substations@ and other stationary applications. This recommended practice is based on commonly accepted methods used to define the load and to ensure adequate battery capacity. The method described is applicable to all installations and battery sizes.The installations considered herein are designed for operation with a battery charger serving to maintain the battery in a charged condition as well as to supply the normal dc load.This recommended practice was prepared by the Battery Sizing Working Group of Standards Coordinating Committee 29 (SCC29). It may be used separately@ but when combined with IEEE Std 450-1995@ IEEE Recommended Practice for Maintenance@ Testing@ and Replacement of Vented Lead-Acid Batteries for Stationary Applications@ and IEEE Std 484-1996@ IEEE Recommended Practice for Installation Design and Installation of Vented Lead-Acid Batteries for Stationary Applications@ it will provide the user with a general guide to designing@ placing in service@ and maintaining a lead-acid battery installation.This recommended practice describes methods for defining the dc load and for sizing a lead-acid battery to supply that load for stationary battery applications in full float operations. Some factors relating to cell selection are provided for consideration. Installation@ maintenance@ qualification@ testing procedures@ and consideration of battery types other than lead-acid are beyond the scope of this recommended practice. Design of the dc system and sizing of the battery charger(s) are also beyond the scope of this recommended practice.