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In this work, supercapacitor or ultra‐capacitor cells are composed of active carbon material (ACM) having BET specific surface area of 1133 m2 g−1. The ACM is prepared by carbonizing waste biomass (mango kernel) at 900°C. To develop high porosity in ACM, potassium hydroxide was used as an activating agent. Porous morphology of the synthesized ACM is explored through Scanning Electron Microcopy. Thereafter, two supercapacitor cells have been composed by using the mentioned ACM (electrode material) and KOH 6 M & NaOH 1 M (electrolytes). Applicability of the electrode material for supercapacitor has been tested electrochemically through the standard CV, EIS, and CD techniques. Observed capacitive assets from CV curve at 5 mV s−1 was 151.5 F g−1 (with KOH 6 M) and 133 F g−1 (with NaOH 1 M). Experimentally obtained impedance data from EIS technique were compared and fitted theoretically by utilizing Randles fitting circuit. By taking frequency into consideration, it is found that the KOH 6 M based cell is providing lower time constant value and supporting better diffusion process than NaOH. Analysis of CD curve at 1.1 A g−1 have given the capacitance of 136.5 F g−1 and corresponding energy and power density of 12.1 Wh kg−1 and 930 W kg−1. In addition to this, the small voltage drop and low ohmic resistance observed with KOH based system suggests its better capacitive assets than NaOH based supercapacitor system. Moreover, good capacitance retention of 85% is observed in a 2000 life cycle test. [ABSTRACT FROM AUTHOR]