This paper presents the discovery on proton conducting biopolymer electrolyte (BPE) by incorporating various NH4Br composition (wt%) with biopolymer materials carboxymethyl cellulose (CMC) which has been prepared via solution casting method. The biopolymer–salt complex formation has been analyzed through Fourier Transform Infrared (FTIR) spectroscopy, Thermo Gravimetric Analysis (TGA), impedance and transference number measurement (TNM). The highest ionic conductivity at ambient temperature is 1.12×10−4 S cm−1 for sample containing 25wt% NH4Br. It has been shown that the conducting element in this work are predominantly due to proton (H+) which was confirmed via FTIR and TNM analysis. Rechargeable proton conducting BPE battery have been fabricated with the configuration of Zn+ZnSO4.7H2O/BPE/MnO2 and produced a maximum open circuit potential (OCP) of 1.36V at ambient temperature and showed good rechargeability. This work implies that the possible practical application of the present electrolytes as a new invention in the fabrication of electrochemical devices.