The charge voltage of the battery pack must be maintained at a constant value. At this voltage, the charge amount should be sufficient to cover the loss of self-discharge and the requirement of oxygen circulation, to ensure the battery is in a fully charged. And the selection of the voltage of recharge should consider battery overcharge to minimize the impact of battery damage, this voltage is called floating voltage, under normal circumstances (20 ~ 30 °C), the battery float voltage is 2.25V / monomer.