Boy, the battery manufacturing industry is so confusing. I just spent an hour going down the rabbit hole and don't quite know what I can conclude from it...
First, this article supposedly tells us the history of Durastart...
North40 Outfitters article about DuraStart
It gives us factory locations of Berks County PA and Corydon, IA and has family names of the founders. And it also mentions a trademarked technology, IPF. But a little more looking tells us that's all East Penn Manufacturing info. The Bridegam family, the manufacturing facilities, the IPF trademark... that's all East Penn Manufacturing (the manufacturer of Deka batteries).
But then I saw this article which brings Exide into it....
Exide partners with ShowMeParts for MidStates Distributors
This one clues us into the DuraStart label and explains why a web search for DuraStart batteries brings up so many farm-and-home stores. It tells us the DuraStart label belongs to MidStates Distributing Co., a cooperative of 43 independent farm, ranch, and home retailers across the US and Canada. And it tells us MidStates partnered with Exide for the label. That suggests the batteries would be Exide batteries.
So where does that leave us?
It appears the batteries offered by your local guy MAY have been manufactured by East Penn. There may be some clues from looking closely at the photos of the cases, terminal layouts, etc, and comparing to photos of East Penn and Exide batteries.