The results of R&D work on nuclear batteries of the capacitor-type with a liquid electrolyte are reported. A high-porosity carbon matrix containing the radioactive isotope 90Sr is used in one of the electrodes of the new type of nuclear batteries. Ionic liquids, where the charge carriers are free ions formed on dissociation of ionic pairs of the ionic liquid on account of the kinetic energy of the β-particles of 90Sr, are used as the electrolyte. The charges are separated by a double electric layer at the boundary of an electrode and liquid electrolyte similarly to supercapacitors.