Sealed Lead Acid is a generic term for all lead acid batteries which have fixed tops. The electrolyte is supplied with the battery when it’s manufactured, and it\’s not intended that the battery ever be opened or topped up in the field. All lead acid batteries must have vents to allow any excess gas pressure to escape from the battery casing. Lead acid batteries should, in general, never be charged in a completely sealed cabinet or enclosure, for this reason. Valve regulated batteries release little to no gas during charge and discharge, as they are designed to operate with a small positive gas pressure inside the battery casing. Gel cell batteries have the acid electrolyte in the form of a gel. If the battery plastic casing is damaged in transit or in an accident, the electrolyte is not in liquid form and can’t run out the battery or cause further damage. However, gel batteries are more easily damaged by overcharging, because gas bubbles form in the gel and may push the electrolyte away from the plate surface, permanently reducing the capacity. Absorbed electrolyte type have the acid in liquid form, trapped in a glass fibre mat between the plates. There’s not much difference in discharge performance between batteries, but there is often a difference in recharge voltage limit. It is advisable to check the battery manufacturer’s spec for recommended constant voltage charging range before charging.