Aargh. I can't take it any more. _All_ types of batteries being discussed are lead-acid batteries. Sealed lead-acid batteries are lead-acid, AGM's are lead-acid, gel-cells are lead-acid, and normally vented liquid electrolyte lead-acid batteries are lead-acid.
The differences between them are the physical construction of the case (open vents vs. pressure relief valves) and the physical form of the electrolyte (liquid, silica-gel, or liquid-soaked-fiberglass).
They all use lead-acid chemistry.