Continue to charge is an overcharge procedure when a battery has been fully charged. At this time the Ni(OH)2 of positive electrode had become NiOOH, the battery voltage reaches a balance value(maximum value). Continued charge will oxide OH- into oxygen. The formed oxygen permeate separator and compound with the negative electrode. This chemical combination reaction generates large amount of heat, so the temperature of total battery system increases sharply. The more high temperature, the more low balance voltage, that is temperature increases will lead to balance voltage decreases, so the battery voltage will decrease after it had been fully charged.