I teach battery technology so I think I can bring some light to this subject. Bear with me, the explanation is long...

Optima batteries are designed in a way that they should not receive greater than 7 amps of charge. They will deal with a greater amount for a SHORT period of time but is NOT recommended! The reason for the limit on charging is due to it's construction. Each spiral cell is a continuous roll of perforated lead covered on both sides as it's rolled up with fiberglass matting and paste. Once they are installed in the case and connected to the posts, a specific amount of water and acid is added. The solution is absorbed by the matting and held next to the rolled lead plates. Now, the reason for the limiting of charging is due to potential evaporation of the water in the solution. If over charged, the water evaporates and once the pressure in the case reaches a certain pressure, the release valves in the top of the case (the two "stone" looking things) open. Once the pressure is released, and an amount of water leaves with it, the life of the battery is done (the valves do NOT reset).
There are now chargers that are designed for AGM (Absorbed Glass Material) batteries.

I hope this helps