Battery-supercapacitor hybrid (BSH) devices combine the high energy density of batteries with the high power density and long cycle life of supercapacitors. These devices are designed to meet the demands of future applications such as electric vehicles, smart grids, and wearable electronics. BSHs typically consist of a high-capacity battery-type electrode and a high-rate capacitive electrode. This review discusses the fundamental principles, structure, and classification of BSHs, as well as recent advances in various types of BSHs, including Li-/Na-ion BSHs, acidic/alkaline BSHs, BSHs with redox electrolytes, and BSHs with pseudocapacitive electrodes. The review also highlights recent progress in BSHs with specific functionalities such as flexibility and transparency. It discusses future trends, challenges, and proposes two conceptual BSHs with aqueous high voltage windows and integrated 3D electrode/electrolyte architectures. The review covers the design considerations, structure, and classification of BSHs, including the distinction between SC electrodes and battery electrodes. It discusses the energy storage mechanisms of BSHs, the role of electrolytes, and the performance of various BSH types, including Li-ion, Na-ion, acidic, alkaline, and redox electrolyte BSHs. The review also highlights recent advances in materials and performance, including the development of nanostructured electrodes, the use of pseudocapacitive materials, and the optimization of electrolytes for improved performance. The review concludes with a discussion of the future prospects and challenges of BSH technology.Battery-supercapacitor hybrid (BSH) devices combine the high energy density of batteries with the high power density and long cycle life of supercapacitors. These devices are designed to meet the demands of future applications such as electric vehicles, smart grids, and wearable electronics. BSHs typically consist of a high-capacity battery-type electrode and a high-rate capacitive electrode. This review discusses the fundamental principles, structure, and classification of BSHs, as well as recent advances in various types of BSHs, including Li-/Na-ion BSHs, acidic/alkaline BSHs, BSHs with redox electrolytes, and BSHs with pseudocapacitive electrodes. The review also highlights recent progress in BSHs with specific functionalities such as flexibility and transparency. It discusses future trends, challenges, and proposes two conceptual BSHs with aqueous high voltage windows and integrated 3D electrode/electrolyte architectures. The review covers the design considerations, structure, and classification of BSHs, including the distinction between SC electrodes and battery electrodes. It discusses the energy storage mechanisms of BSHs, the role of electrolytes, and the performance of various BSH types, including Li-ion, Na-ion, acidic, alkaline, and redox electrolyte BSHs. The review also highlights recent advances in materials and performance, including the development of nanostructured electrodes, the use of pseudocapacitive materials, and the optimization of electrolytes for improved performance. The review concludes with a discussion of the future prospects and challenges of BSH technology.