Aqueous zinc-ion hybrid supercapacitors are a promising energy storage technology, owing to their high safety, low cost, and long-term stability. At present, however, there is a lack of understanding of the potential window and self-discharge of this aqueous energy storage technology. This study concerns a systematic investigation of the potential window of this device by cyclic voltammetry and galvanostatic charge-discharge. Hybrid supercapacitors based on commercial activated carbon (AC) demonstrate a wide and stable potential window (0.2 V to 1.8 V), high specific capacitances (308 F g-1 at 0.5 A g-1 and 110 F g-1 at 30 A g-1 ), good cycling stability (10000 cycles with 95.1 % capacitance retention), and a high energy density (104.8 Wh kg-1 at 383.5 W kg-1 ), based on the active materials. The mechanism involves simultaneous adsorption-desorption of ions on the AC cathode and zinc ion plating/stripping on the Zn anode. This work leads to better understanding of such devices and will aid future development of practical high-performance aqueous zinc-ion hybrid supercapacitors based on commercial carbon materials, thus accelerating the deployment of these hybrid supercapacitors and filling the gap between supercapacitors and batteries.