Charging a battery usually involves completing two tasks: first, restoring the battery to its rated capacity as quickly as possible, and second, using low current charging to replenish the energy lost by the battery due to self discharge to maintain its rated capacity. During the charging process, lead sulfate gradually precipitates from the negative electrode plate of lead-acid batteries, while lead sulfate on the positive electrode plate gradually generates lead dioxide. When the lead sulfate on the positive and negative plates completely forms lead and lead dioxide, the battery begins to undergo overcharging reactions, producing hydrogen and oxygen. In this way, in unsealed batteries, the water in the electrolyte will gradually decrease. In sealed lead-acid batteries, hydrogen and oxygen can recombine into water at a moderate charging rate. The start time of overcharging is related to the charging rate. When the charging rate is greater than C/5, the overcharging reaction begins before the battery capacity recovers to 80% of the rated capacity. Only when the charging rate is less than C/100 can the battery experience overcharging reaction after the capacity is restored to 100%. In order to restore the battery capacity to 100%, a certain amount of overcharging reaction must be allowed. After the overcharging reaction occurs, the voltage of the single cell battery rapidly increases. After reaching a certain value, the rate of increase decreases, and then the battery voltage begins to slowly decrease. From this, it can be seen that the best way to maintain capacitor capacity after the battery is fully charged is to add a constant voltage to both ends of the battery pack. Under float voltage, the charged current should be able to supplement the energy lost by the battery due to self discharge. The float charging voltage should not be too high to avoid shortening the battery life due to severe overcharging. By using appropriate float charging voltage, the lifespan of sealed lead-acid batteries can reach over 10 years. Practice has shown that when the actual float charging voltage differs by 5% from the specified float charging voltage, the lifespan of maintenance free batteries will be shortened by half. The voltage of lead-acid batteries has a negative temperature coefficient, with a single cell value of -4mV/℃. A normal (non temperature compensated) charger that works ideal at an ambient temperature of 25 ℃. When the ambient temperature drops to 0 ℃, the battery cannot be fully charged. When the ambient temperature rises to 50 ℃, the battery's lifespan will be shortened due to severe overcharging. Therefore, in order to ensure that the battery can be fully charged over a wide temperature range, the various conversion voltages of the charger must vary with the temperature coefficient of the battery voltage.

• Charging characteris…