All Optimas are AGM type batteries.
AGM = Advanced Glass Mat
The Gel electrolyte is suspended in a fiberglass mat that is spiral wrapped between ribbons of the electrode material.
They ahave a lower internal resistance ( think capacitors in high power audio systems ) & take a charge quicker & release the electricity quicker.
AGM batteries use the identical charging voltage & rates as a lead acid batteries. The only "car" type battery that requires different charging schemes is a "Gel Cell".
Dollar for dollar, an AGM is the best heavy duty battery.

Now, if you look in your yello pages under Batteries, or Auto Electrical, you will find your local Interstate dealer & many others. Ask if they might have any "Seconds" in the AGM series.

I bought 36 of the 31 series for a boat 9 years ago & they were on the shelf for 2 years. Royal sold them to me for $52.00 each. They are still working just fine. It is an ocean cruising 65 Morgan Outisland & the batteries are all mounted in the keel. THe boat sees shore power 6% of the time. Otherwise, Alternator, Solar & Wind gen keep them going. Draws are tremendous.... 6 12V A/C units, 2 12V reefers, 2 12V freezers, 6 laptops, full suite of electronics w 3 backups for each, 12VB auto furlers, 12v winching systems for all sail controls, 2 bow thrusters.

Boat has done Dartwin's trip 3 times so far....

AGMs RULE.

Ed