A substrate-integrated nickel–iron ultra-battery is realized using nickel oxide (NiO) nano-flakes and hematite (α-Fe₂O₃) nano-rods as electroactive materials for its positive and negative electrodes, respectively. Direct growth of electro-active materials on highly-conductive stainless steel substrate enhances mechanical stability of the system together with the reduction in its internal resistance. The proposed nano-architectural design of the electroactive materials provides large number of interaction sites for the electrolytic ions with the electrode materials in conjunction with short ion-diffusion paths, which significantly improve the capacitive performance of individual electrodes and hence of the fabricated ultra-battery. As a consequence, hematite nano-rod electrode exhibits a maximum specific capacity of ~ 45 mAh/g (191 F/g) at a current density of 1 A/g while NiO nano-flake electrodes are found to have specific capacity of ~ 51 mAh/g (366 F/g). The as assembled ultra-battery has the specific capacity value of ~ 36 mAh/g (94 F/g and volumetric capacitance ~ 0.77 F/cm³) at a current density of 0.5 A/g in a potential window between 0V and 1.4 V, with capacitance retention of ~ 60 % of its original value when the load current-density is increased 20 times. More importantly, maximum energy and power density values achieved with the ultra-battery are ~ 25 Wh/kg and ~7 kW/kg, respectively, which are superior to other recently reported pristine nickel, iron and other transition metal/metal oxide-based energy storage devices.