Interstate batteries are made by Johnson Controls, which makes 65% of the car, truck, and marine batteries
in the US. They also make batteries for Walmart, and Autozone. They use to make Kirkland batteries for Costco, which now sells Interstate batteries. For the price, and their return/exchange policy, an Interstate battery from Costco is hard to beat.
Sorry Riddler, this doesn't really help you, since you need an AGM battery.
I had one of those reproduction AGM batteries. Was heavy as heck, lasted about 5 years.
Was very expensive.