Proper charging of pure lead batteries is essential to ensure their optimal performance and longevity. There are several effective charging methods available for these batteries.

One commonly used method is constant voltage charging. This technique is highly recommended for pure lead batteries as it helps maximize the battery's capacity and service life. In this approach, a high charge current initially flows into the discharged battery. As the battery picks up the charge, the current gradually drops off until the power supply reaches a pre - set voltage. Once the battery attains this voltage, the current reduces to a minimum value. For example, in standby service applications, the recommended voltage is typically set between 2.23 - 2.30 volts per cell at a temperature range of 20 °C (68 °F) to 25 °C (77 °F). In cycle service, the voltage range is slightly higher, from 2.40 - 2.50 volts per cell within the same temperature range. It's crucial to set the charge voltage accurately according to the specified charge and temperature characteristics. Incorrect voltage settings can lead to overcharging or undercharging, which can significantly degrade the battery's performance and lifespan. One advantage of constant voltage charging is that it allows the battery to be left connected to the charger until needed. The battery's "float voltage" remains constant as trickle charging continues to compensate for normal self - discharge.

Another method is constant current charging. In this method, the lead - acid batteries are connected in series to form groups, and each group charges from a main direct current (DC) supply unit via a loading rheostat. The charging current remains constant throughout the process by adjusting the circuit resistance as the battery voltage rises. To prevent overheating or excessive gas generation, constant current charging can be carried out in two steps: initially with a high charging current and then a low current towards the end of the charging process. However, this method has its drawbacks. It requires careful monitoring as if the battery is overcharged, it can overheat, leading to premature failure. Also, the charge time for the battery is relatively long compared to some other methods. Therefore, it's often necessary to use a timer function or closely monitor the charging process to ensure the battery is disconnected at the right time.

The constant current constant voltage (CC/CV) charging technique combines elements of both constant current and constant voltage charging. First, the battery charger limits the current to a pre - set level until the battery reaches a pre - set voltage. After that, as the battery approaches full charge, the current decreases. This method typically charges the battery in three steps. The first step is the constant current charge, also known as the bulk charge, which fills about 70% of the battery's capacity in 5 - 8 hours. The second step is the topping charge, where a low - current trickle charge is applied to fully saturate the battery. This step is crucial for maintaining good battery health as a battery that is continuously under - charged can experience sulfation, reducing its ability to hold a charge. The final step is the float charge, where the battery's float voltage reduces to compensate for self - discharge, ensuring the battery remains fully charged. Although this method can improve the battery's maximum service life and capacity, it does have a relatively long charge time, and there can be issues such as corrosion or excessive hydrogen gas buildup in some cases.

Taper current charging is a simpler and more cost - effective method but is generally not recommended for pure lead batteries as it can sacrifice the battery's life cycle. This method involves applying a constant voltage or current to the battery through transformers, where the transformer's resistance limits the charge current available to the battery. As the battery voltage rises, the current demand reduces. However, due to its potential negative impact on the battery's lifespan, it should be used with caution, and in some cases, additional measures like limiting the charging time or incorporating a charging cut - off circuit may be necessary to prevent over - charging.