or HD FXRG Boots are Wolverine, HD Heated Gloves are Gerbing..the list goes on and on and on...they are the king of marketing and who can blame them for making money that way and being successful..just we don't have to pay for the bar and shield logo if we don't want to

I wouldn't trust the online store..I would be shocked it they don't offer OEM AGM replacements

The part number for the oem Harley battery is 66010-97E for $157 but doesn't seem to be available. Maybe the motor company IS only selling lithium. If so buy the Deka, , as many have surmised that it's what HD is putting in these bikes. It does make sense since they're manufactured in Lyons , pa which is just an hour away from the York assembly plant. Plus they're American made although I don't know if Harley cares too much about that. It's interesting that they've been using the same battery since 97.

I’ve had really good luck with the Super Start batteries at O’Reilly Auto Parts. I believe it’s an East Penn rebranded product….

Yes, I was very surprised too. It's not like a 2015 model year bike is ancient and no longer supported. LOL.
The manager of one of the Batteries Plus stores close to my house suggested a Lithium for my bike too. But also, when I asked about an AGM replacement they sell, he said it was from the East Penn Plant too, just labeled Duracell. AS I recall though, it wasn't significantly lower in price than the Harley version.

About the Wolverine boots and HJC helmets, you are right. Those are just Wolverine and HJC relabeled with Harley Graphics. There isn't any special customization built-in for Harley specs. AS far as the batteries being special customized, I don't know.

Dealers will have the 66010-97E, just not possibly listed online. Kinda like being able to find oil or oil filters online without having to buy the whole oil change kit.

This Yuasa battery is manufactured in the USA and is 500 CCA versus the OEM 400 CCA. I had one on my ’03 Ultra.
Yuasa GYZ32HL

https://www.yuasabatteries.com/battery/gyz32hl/

Mega Crank from Battery Mart $110 shipped to your home and it’s more powerful then anything from HD

Yuasa is a GREAT battery, 500 CCA and a favorite except their price went through the roof, not sure if it was Covid related but not worth to me 75% price premium over the Mega Crank.

Which model?

The mega crank from battery mart is made overseas. You'd have to order the big crank at 130 to get one made here if that matters to you. The Deka battery from Lowes is still the best buy at 106 but they do charge tax which battery mart doesn't.