The process of applying aircraft batteries to gas turbine engine starting systems has long been either by trial and error or by a rather lengthy, drawn-out analytical process.A convenient descriptive value for the battery characteristic, which is significant in engine starting, is now available. This characteristic is conveniently evaluated for any battery design using relatively simple equipment. This measurement is then self-sufficient for determining the engine starting performance of that battery.This paper discusses a convenient measurement for describing the gas turbine engine starting capability of nickel-cadmium batteries and the usefulness of that measurement in applying a battery to a starting system.A description of the measurement of the power delivery capability of a battery is presented, along with a discussion of the reasoning for selection of the secondary rating conditions. The results of an evaluation of the engine starting requirements of the Beech E-90 are presented. Those results demonstrate the usefulness of this technique to describe the battery needs for an existing system. Only by accurate description of the true requirements of various applications can the development efforts of battery manufacturers be brought to bear on filling those requirements in an optimum manner.