Got a Duracell from Sam's Club. Group 34, 800 CCA, positive terminal on the left like the original. It was $108. They had the same battery that was AGM. $70 more. I'm sure like everything else it's gone up. But it fit perfectly.
Be careful running agm, most have a low maximum charging voltage and most vehicle alternators produce high enough voltage to damage most agm batteries on the market. I haven't dug up the ratings on the roxor alternator yet, but I would bet its not compatible with agm batteries.
I haven't looked at the operation of the charging system on the roxor, but it is possible the ones that come with an agm battery have a voltage limited charging system. If I was considering an agm, I would verify the ratings were compatible for peace of mind. I'm also a cheap ass and would be disappointed if I cooked a $200+ battery from not taking the time to research what I was working on.