The current distribution in the positive current collector of a Na/Se(IV) battery has been studied by measuring the potentials of selenium reactions with inert tungsten microelectrodes. The radial potential distribution on discharge depended on the arrangement of the positive current collector and the conductivity of the graphite felt. A high reaction rate near the beta" -alumina tube observed in a cell with a homogeneous current collector could be inhibited by a dual-mat design composed of a thin inner felt with high resistivity and bulk felt with high conductivity. Precipitation of sodium chloride on discharge influenced the current distribution and the polarization as well as the capacity.