Marine battery are generally of two types. Each type of battery has its different workings. A marine starting battery is used only for the purpose of starting the boat engine whereas a deep cycle marine battery is used for the other power requirements. These are available during a sealed form which makes them leak resistant and maintenance free. The most commonly used is the lead Marine battery which is filled with an electrolyte solution of euphoric acid and can store relatively large amounts of power without taking up too much space. These batteries can further be categorized in three types.
The flooded cell or wet cell batteries are the most inexpensive and also the most popular. They work by immersing lead plates in a euphoric acid electrolyte solution. These Marine battery need to be taken good care of and also occasional replenishment of the electrolyte solution which is why they are not sealed. They can be prone to leaks and also the generation of hydrogen which is highly explosive unless the battery compartment is properly vented. Very precautionary measures must be taken in handling the battery. You must also be careful not to let the electrolyte come in contact with the skin as it can cause burns. Additionally, if the electrolyte comes in contact with seawater, toxic chlorine gas can be generated.
Marine battery batteries use a gel like silica to stabilize and thicken the electrolyte solution. This way, even if there is a crack in the battery casing, there is no leak of electrolyte and the battery will continue functioning. Because no maintenance is required, these batteries are generally sealed but you need to be careful when charging them lest they be damaged. These batteries also reduce the electrolyte evaporation. They are also chemically similar to the wet cell batteries. They are also more expensive than wet cell batteries.