Battery charging is usually done to complete two tasks, first of all as soon as possible to restore the rated capacity of the battery, the other is the use of small current charging, recharge the battery due to self-discharge loss of energy to maintain the rated capacity of the battery. In the charging process, lead-acid battery lead on the lead gradually lead sulfate lead, lead plate on the lead gradually lead dioxide. When the lead and lead on the positive and negative lead completely generated lead and lead dioxide, the battery began to charge reaction, resulting in hydrogen and oxygen. In this way, in the non-sealed battery, the water in the electrolyte will gradually decrease. In sealed lead-acid batteries, hydrogen and oxygen can be re-combined into water when a medium charge rate is used. The time of overcharge is related to the rate of charging. When the charge rate is greater than C / 5, the battery capacity returned to 80% of the rated capacity, that is, began to overcharge reaction. Only the charge rate is less than C / 100, in order to make the battery back to 100% capacity, the emergence of overcharge response. In order to restore the battery capacity to 100%, must be allowed to a certain overcharge reaction. After the overcharge reaction occurs, the voltage of the single cell battery rises rapidly, reaching a certain value, the rate of increase decreases, and then the battery voltage begins to drop slowly. It can be seen, the battery is fully charged, the best way to maintain the capacitance is to add a constant voltage across the battery pack. Floating charge, the charge current should be able to recharge the battery due to self-discharge and loss of energy. Float voltage can not be too high, so as to avoid serious overcharge and shorten battery life.