Battery systems based on alkali metal anodes and solid solution cathodes, ie, cathodes based on the insertion of the alkali cation in a" host lattice," show considerable promise for high energy density storage batteries. This paper discusses the interaction between battery requirements, in particular for vehicle propulsion, and electrochemical and constructional factors. It is argued that the energy obtainable at a given load is limited by saturation of the surface layers of cathode particles with cations, and that the time before saturation occurs is determined by diffusion of cations and electrons into the host lattice. Expressions are developed for plane, cylindrical, and spherical particles, giving the relation between battery load and the amount of cathode material utilized before saturation. The particle shape and a: single parameter Q is used to describe cathode performance. Q is the ratio between discharge time at 100% utilization of the cathode at the given load, and the time constant for diffusion through the cathode particles. This description is extended to cover short peak loads characteristic of vehicle propulsion. On the basis of estimated parameters for the Li/TiS2 couple with LiC104-propylenecarbonate electrolyte the properties of plane cathodes or cathodes consisting of few layers of particles are examined in relation to traction requirements. In this context limiting currents in the electrolyte phase are discussed, and a relation between the maximal allowed values for particle size and electrode spacing is derived. For nonporous electrodes the limiting factor is cathode surface saturation. A qualitative discussion of porous cathodes indicates that the cathode thickness, and thus the over-all specific energy, is limited by cation transport in the pore electrolyte when the cation diffusion coefficient in the solid exceeds 10-10 cm 2 sec-1. On the basis of an approximate relation between cathode thickness and electrode spacing the specific energy for the Li/TiS2 system with organic electrolyte is estimated to be 120-150 W-hr/kg in agreement with published values.