Solid-state battery progress is hindered by a lack of operando methods that monitor charge transport across and between solid-state interfaces. Here, a new electrochemical technique is proposed for operando characterization of all solid-state batteries. The technique is inspired by the established 4-point probe method and operates through insertion of two porous reference electrodes within the solid-state electrolyte. Success would mean the invention of a simple-to-understand technique that is generally applicable to any solid-state battery system or component cell. The defining strength of the proposed technique is that it enables direct measurement, without modeling, of charge transport across and through solid-state battery interfaces. Structural changes can then be related to all relevant charge transport properties, individually. Insight gained using the 4-electrode probe will facilitate solid-state battery commercialization, thereby affording society safer and more efficient energy storage options.