The constant voltage charging method is employed during the charging process, and the voltage remains constant throughout this process, resulting in a high charging current at the beginning, which gradually decreases as charging progresses. This method offers an advantage, as it prevents excessive charging current that could cause the falling off of active substances on the electrode plate, and consequently, the loss of electric energy. However, the initial large charging current may result in changes and shrinkage of active material volume, which could affect its mechanical strength and cause it to deteriorate. Additionally, the small charging current at the later stage of charging may not reach deep into the electrode plate, resulting in long-term insufficient charging that may affect the battery's durability. This charging method is best suited for special occasions without advanced charging equipment, such as the charging of batteries in cars or small dry battery type batteries using the isobaric charging method. Each single battery of alkaline or acid battery requires a power supply voltage of about 1.6-2.0V and 2.4-2.8V, respectively, for efficient charging.