creeker, Go to the Surrette/Rolls and Optima battery sites. Read up on battery construction.
Our normal, everyday lead-acid battery uses a series of plates and separators hung in a sulphuric acid/water electrolyte solution. This is called "flooded cell" or "wet cell" construction. Many other considerations, but that's basic.
The Optimas and several others are AGM - Absorbed Glass Mat - construction, which means that the plates are very tightly packed between glass mats which are soaked in a gelled acid electrolyte. Because the technology is not liquid and requires no venting, the battery may be mounted in any position. Again, a basic difference.
A third variant, the gel-cell battery, runs at a slightly lower voltage and is generally more suited to long term deep discharge work, such as warehouse loaders and golf carts. (BUT, good ol' deep cycle wet cells are still better for those applications.)
The Optima uses six spiral wound AGM cells of 2.2 volts each to make a battery. A battery is composed of a number of cells connected in series. A fully charged "12 volt" battery reads 12.6 volts, unloaded for 4 hours. A dead battery reads 11.8 volts under the same conditions: there's some surface voltage, but not enough amp hour current to accomplish anything.