Researchers created a portable, maintenance-free lead-acid battery in the middle of the 1970s. The wetted separator is filled with the gelled liquid electrolyte, and the enclosure is then closed. Ventilation is made possible via safety valves during charging, discharging, and variations in ambient pressure.
Small sealed lead-acid systems (SLA), also known as Gelcell, and bigger valve-regulated lead-acid systems (VRLA), have both become popular due to varying market demands. The two batteries are comparable. The term “sealed lead-acid” may be regarded by engineers as misleading because no rechargeable battery can be totally sealed.
Because overcharging can result in gassing and water starvation, SLA and VRLA batteries are made with low overvoltage potential, unlike flooded lead-acid batteries. This prevents the battery from reaching its gassing potential during charging. Lead-calcium, rather than lead-antimony, is used in sealed lead-acid batteries to lessen dry-up.