Maintenance free lead-acid batteries are defined relative to traditional batteries that require regular addition of acid and water (such as car batteries). The basic characteristics of maintenance free lead-acid batteries are that they do not require acid or water addition during use. The battery is a sealed structure, does not leak acid, and has no acid mist. The battery is equipped with a one-way exhaust safety valve. When the internal gas pressure of the battery exceeds a certain value, the safety valve automatically opens, exhausts gas, and then automatically closes. Under normal conditions, the safety valve is sealed.