To provide a secondary battery assembly hardly giving rise to short circuit, in one with a plurality of secondary batteries connected in series.

For the secondary battery assembly provided with a plurality of secondary batteries each having a cathode terminal and an anode terminal, inter-electrode connecting members connecting the anode and cathode terminals of the secondary batteries, and an assembly case in which the secondary batteries are serially connected by the inter-electrode connecting members and housed, the plurality of secondary batteries are arrayed for tiptop faces to be in a matrix in a row and column directions, and the secondary batteries are to be connected to each other with the inter-electrode connecting members, so that, provided a ratio of a long side to a short side of the secondary battery tiptop face is 2:1 with the short side set at 1, a length of a side of the secondary battery block is to become either (1) even-number rows times even-number columns, (2) odd-number rows times even-number columns, or (3) even-number rows times odd-number columns, and that adjacent two secondary batteries located at an outer periphery of the secondary battery block are to be ones at the end part connected in series with each other, except when a length of the side of the secondary battery block becomes an alignment of either odd-number rows times odd-number rows and one including two rows or two columns.