A modular battery comprising: a housing, a first planar battery cell having a first planar electrode surface, a second planar battery cell having a second planar electrode surface, and an interconnector disposed between the first planar surface and the second planar surface and electrically connecting the first and second planar electrode surfaces, side peripheries of the interconnector, first and second planar battery cells being electrically insulated from the housing, each of the first planar battery cell and the second planar battery cell including multiple positive and negative electrodes, with each positive and negative electrode (9, 10, 14, 15) electrically connected in parallel to each of the other electrodes of the same polarity, tabs (2, 6) of the positive electrodes (9, 14) of each planar battery cell being connected to each other to form a positive end tab constituting a positive terminal of the planar battery cell, tabs (4, 8) of the negative electrodes (10, 15) of each planar battery cell being connected to each other to form a negative end tab constituting a negative terminal of the planar battery cell, each of the positive and negative end tabs being sealed with an electrically insulating sealant at the opposite edges of the planar battery cells, each of the first planar battery cell and the second planar battery cell including: an interior positive electrode that is coated on both sides with a cathode active material and that has an uncoated positive tab on one side; an interior negative electrode that is coated on both sides with an anode active material and that has an uncoated tab on the opposite side to the positive tab; a positive end-electrode that is coated on one side only with a cathode active material and that has two bare foil tabs; and a negative end-electrode that is coated on one side only with an anode active material and that has two bare foil tabs. a housing, a first planar battery cell having a first planar electrode surface, a second planar battery cell having a second planar electrode surface, and an interconnector disposed between the first planar surface and the second planar surface and electrically connecting the first and second planar electrode surfaces, side peripheries of the interconnector, first and second planar battery cells being electrically insulated from the housing, each of the first planar battery cell and the second planar battery cell including multiple positive and negative electrodes, with each positive and negative electrode (9, 10, 14, 15) electrically connected in parallel to each of the other electrodes of the same polarity, tabs (2, 6) of the positive electrodes (9, 14) of each planar battery cell being connected to each other to form a positive end tab constituting a positive terminal of the planar battery cell, tabs (4, 8) of the negative electrodes (10, 15) of each planar battery cell being connected to each other to form a negative end tab constituting a negative terminal of the planar battery cell, each of the positive and negative end tabs being sealed with an electrically insulating sealant at the opposite edges of the planar battery cells, each of the first planar battery cell and the second planar battery cell including: an interior positive electrode that is coated on both sides with a cathode active material and that has an uncoated positive tab on one side; an interior negative electrode that is coated on both sides with an anode active material and that has an uncoated tab on the opposite side to the positive tab; a positive end-electrode that is coated on one side only with a cathode active material and that has two bare foil tabs; and a negative end-electrode that is coated on one side only with an anode active material and that has two bare foil tabs.