Schumacher"s X-Line Batteries are sealed maintenance-free AGM lead-acid batteries. AGM batteries excel in cycling performance, severe service durability, deep discharge resiliency, and vibration resistance. This battery type has the following characteristics: Maintenance-free, leak-proof and position insensitive. Batteries of this kind have a safety vent to release gas in case of excessive internal pressure build-up. AGM (absorbed glass mat) refers to a specific type of SLA/VRLA battery where the electrolyte is absorbed into separators between the plates consisting of sponge like fine glass fiber mats.