In Fig. , it can be obviously seen that the batteries in electrolyte with the addition of H 2 SO 4 have higher capacity than battery in pure 1MZnSO 4 electrolyte. The charging capacity of battery refers the amount of active material which can be oxidised during the charging process. The low charging capacity in Fig. (a) may be caused by the loss of active material under the influence of decomposition of NHPI during the charging process. This proves that the acidic environment can improve the persistency of NHPI. It is worth noting that although Fig. ) and (e) both show higher charging capacities, but in discharge process, only battery in ZnSO 4 + 0.05MH 2 SO 4 (pH = 1.26) electrolyte has better capacity retention, which is more than twice of the discharge capacity of the battery in the 1MZnSO 4 +0.1MH 2 SO 4 (pH = 0.99) electrolyte. Furthermore, from Fig. ) and (f), the decreasing of the capacity of batteries can be observed. Among them, the charging capacity of battery in ZnSO 4 + 0.05MH 2 SO 4 (pH = 1.26) electrolyte exhibits a gentle descent curve. The battery with 1MZnSO 4 electrolyte experienced a fall between the first and the second cycle, this may be due to the production of PINO from the first cycle lead to the irreversible reaction between PINO and NHPI to build the oligomer. Thus, the charging from the second capacity starts to become very low due to the loss of NHPI. In Fig. (f), it can be found that the charging capacity profiles also dropped significantly as the function of cycle number. This also meets the previous analysis results for the GCPL chart. The columbic efficiency in Fig. can further verify that the battery has the best performance in 1MZnSO 4 + 0.05MH 2 SO 4 electrolyte. This phenomenon may be caused by the fact that the zinc electrode cannot survive in an electrolyte with too low acidity. During the constant current charge and discharge of the battery, the formation of bubbles on the glass carbon electrode and the corrosion of the zinc electrode were observed, which also confirmed that the zinc electrode spontaneously discharged in the acid electrolyte. Fig. shows the corrosion of zinc anode in the electrolyte. It can be clearly seen that the zinc electrode in 1MZnSO 4 + 0.1MH 2 SO 4 (pH = 0.99) electrolyte has been corroded.