Maintenance free: Open batteries produce gas and leak into the air during the charging process, while the electrolyte moisture decreases. So acid needs to be added regularly. With the sealed valve-regulated design of AGM batteries, the gas produced by internal water decomposition can be recombined back into the electrolyte during the discharge process, without the need to refill the electrolyte regularly. This makes it safe and reduces the labor cost required for maintenance. http://www.jxbattery.com/