The kinetic or activation overvoltage of the reduction and oxidation reactions of the battery should be as small as possible, since during charging the voltage required will greater than the equilibrium voltage by activation energy. The difference in the charging voltage and the discharging voltage (i.e., the overvoltage) reduces the battery efficiency.

If there are secondary or side reactions in the battery, then the kinetic overpotential has different effects between charging and discharging. During discharging, the battery voltage is lower, and therefore there is less possibility that the voltage is sufficient to overcome the activation energy of secondary battery reactions. During charging, the battery voltage is higher, and hence there is the possibility that additional reactions can occur. This effect can give rise to beneficial properties. The hydrolysis of water consists of the redox reaction shown below, which has a electrochemical potential of 1.23 V.

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Consequently, if a voltage of more than 1.23V is applied to a battery which has water as a component of the electrolyte, then the electrolysis of water occurs, producing hydrogen and oxygen instead of the charging reaction for the battery. Since most batteries operate at about 2V, this would then make water-based electrolytes unsuitable for batteries. However, the overvoltage of the redox reactions in the electrolysis of water are high enough such that during discharging, gas evolution from the electrolysis of water (or either one of the half reaction involved in the electrolysis of water) is not a dominant consideration. However, during charging, the higher voltage experienced by the battery causes first the hydrogen and then the oxygen half reactions to proceed. In lead acid battery systems, the presence of these two reactions gives rise to gassing. In many battery configurations, gassing leads to numerous undesirable side-effects, including water loss from the electrolyte and physical damage to the electrolyte.