Banana peels, a common fruit waste was adopted as a material precursor in this study to synthesize highly porous activated carbon from banana peels (ABP) which serves as an electrode material for a symmetric supercapacitor device. The activation was done using KOH pellets at different carbonization temperatures ranging from 750 °C to 950 °C. The ABP sample obtained from the 900 °C carbonization temperature (ABP900) exhibited unique material properties such as hierarchical porous nano-architecture containing micropores, and mesopores with the highest specific surface area (1362 m2 g−1). Electrochemical performance investigation in different neutral aqueous electrolytes showed that the best response was obtained in NaNO3 for the ABP900 electrode. The symmetric device subsequently assembled using 1 M NaNO3 operated in a potential window of 1.8 V, exhibited a specific capacitance of 165 F g−1 with a corresponding energy density of 18.6 W h kg−1 at 0.5 A g−1. A 100% capacitance retention and columbic efficiency were obtained after 10000 continuous charge-discharge cycles at 5 A g−1. Remarkably, after subjecting the symmetric device to a voltage holding test for 60 h, the specific capacitance was observed to increase from 165 F g−1 to 328 F g−1 with a corresponding increased energy density to about 36.9 W h kg−1 at 0.5 A g−1, suggesting a 98% increase in device energy density from its initial value after voltage holding. Thus, the results reported showcase the ABP900 material as a potential nanostructured porous material useful in the design of high-performance electrodes for stable electrochemical capacitors.