The problem of use discharge and noise characteristic of primary power sources system of thionyl chloride/lithium for definition of their operative conditions (first of all, depth of discharge) is considered. On the basis of the analysis of features of discharge curves of Li/SOCl2 cells both bobbin and wound (rolled) type, and also intensity of voltage fluctuations and power-density spectrum of electrochemical noise of above mentioned cells it is drawn a conclusion on an opportunity of carrying out their correct diagnostics.