There is a lot of confusion as to exactly how sealed lead acid batteries are constructed. 

The construction of sealed lead acid batteries is in actual fact it is not as complicated as people may let you believe.  The following is a short piece on exactly how these batteries are constructed.

The whole ethos of how the battery construction is designed is basically to eliminate the loss of electrolyte through evaporation, gassing or spillage.  The basic premise that the batteries are sealed leads to a longer battery life and also reduces the amount of maintenance needed compared to other varieties of batteries.  Other types of batteries have simple valve caps to let gas escape from the batteries, whereas sealed lead acid batteries are constructed using pressure valves which open in extreme conditions.  To reduce the release of oxygen and hydrogen in the air by galvanic action as the sealed lead acid battery is charging the electrolyte needs to have an adapted design.  The electrolyte is designed in sealed lead acid batteries in such a way that it triggers the oxygen and hydrogen to re-amalgamate into water and is often known as a recombinant technique.  Because of the reasons given above and the sealed nature of the batteries, sealed lead acid batteries are much safer than other variants of batteries and are used for mobility scooter battery requirements.