Maintenance-free batteries refer to batteries that do not require maintenance work such as adding electrolyte during their service life (usually four years). Its English name is Mananceeebaey, hereafter referred to as Mbattery. The structure of the maintenance-free battery has the following characteristics: 1. The electrode grid is made of lead-calcium-tin alloy, which completely eliminates the side effects of antimony. Batteries made of low-antimony alloys containing lead (2%-3% antimony) are called maintenance-free batteries. The presence of antimony not only precipitates from the positive electrode and migrates to the surface of the negative electrode during the electrochemical reaction, creating conditions for self-discharge, but also reduces the electromotive force of the battery, increases the charging current, and speeds up the electrolysis of water. 2. Using bag-type polychloroacetic acid separators, the positive plate is installed in the separator bag to prevent the active material from falling off and the plate from short-circuiting. 3. The exhaust plug adopts a new safety exhaust device, and the exhaust plug is equipped with an alumina filter and a palladium catalyst. The filter can prevent water vapor and sulfuric acid gas from passing through, avoid direct contact with external sparks, and prevent explosions. The palladium catalyst helps the exhausted hydrogen and oxygen ions combine to form water, which is then returned to the battery, thereby reducing water consumption. 4. The single battery is connected through the wall to reduce internal resistance and improve starting performance. 5. The shell is made of polypropylene plastic by hot pressing. There are no ribs on the bottom of the shell. The plate pack is located directly at the bottom of the battery, which can increase the volume of the upper part of the plate, increase the storage capacity of electrolyte, and make the inner wall of the casing thinner.