I've bought the H6 &/or Group 48 battery (Crossfire spec) from Walmart in the past, getting their EverstartMax. Last time I looked in the local Walmart, battery was $149-$150, which is a good price. Just about any Auto Parts store will handle the battery. And sometimes you can get a good buy at local Sam's Club or Costco, if one is close. BatteriesPlus also handles lots of car battery sizes. The last battery I got for my Crossfire came from local O'Reilly's Parts Store (nearest parts store for me). Probably will be where I get future batteries for the Crossfire.

And I don't buy the AGM design battery, as I don't think the extra cost is worth it. Just about any car battery is only good for 4-5 years in a Crossfire. Holds true for most vehicles that have significant power needs. (Note: FYI - There are only a handful of manufacturing firms of car batteries; can't remember you they are but others may chime in. They have contracts with various retailers that sell batteries.) Here's link to an article I found some months back: CLICK.

Good luck with your eBay return claim.