The process of charging and discharging lead-acid batteries is an electrochemical reaction. When charging, lead sulfate forms lead oxide, and when discharging, lead oxide is reduced to lead sulfate. Lead sulfate is a substance that is very easy to crystallize. When the concentration of lead sulfate in the electrolytic solution of the battery is too high or the static idle time is too long, it will "hug" and form small crystals. These small crystals attract the surrounding area. The lead sulfate forms large inert crystals like a snowball. The crystallized lead sulfate can not be reduced to lead oxide when it is charged, but it also precipitates and adheres to the electrode plate, causing the working area of the electrode plate to decrease. This phenomenon is called Vulcanization, also known as aging. At this time, the battery capacity will gradually decrease until it becomes unusable.