An assembled battery comprises mainly multiple non-aqueous secondary cells A and at least one electric device B for voltage detection containing a non-aqueous electrolyte connected to the multiple non-aqueous secondary cells A in series. When a difference in the non-aqueous secondary cell A between a voltage per cell (VA1) at a depth of discharge of 25% and a voltage per cell (VA2) at a depth of discharge of 75% is designated as ΔVA, and a difference in the electric device B between a voltage per cell (VB1) at a depth of discharge equivalent to the depth of discharge of 25% of the non-aqueous secondary cell A and a voltage per cell (VB2) at a depth of discharge equivalent to the depth of discharge of 75% of the non-aqueous secondary cell A is designated as ΔVB, the ΔVB of electric device B is greater than the ΔVA of non-aqueous secondary cell A.