Lead acid batteries are generally classified by application (what they are used for) and by construction (how they are made). The primary application is automotive in which the battery is used for starting and lighting. deep-cycle is another major application but is usually broken down into more specific applications such as RV, golf cars, renewable energy, and marine.
There are two popular construction types: flooded batteries (wet) and VRLA batteries (Valve Regulated Lead Acid). In the flooded types, the electrolyte is a solution of sulfuric acid and water that can spill out if the battery is tipped over. In VRLA batteries, the electrolyte is suspended in a gel or a fiberglass-mat (AGM technology), allowing these batteries to be mounted in a variety of positions.
Before getting started, be sure to identify the type of battery involved.