Inexpensive AGM battery from Chrome Battery fits really well, just needed some padding hot glued to it to make up the size difference. The YTZ7S-BS is shorter, BUT, a little wider so the plates have more surface area providing higher CCA. The boot actually works when you use it in a top mount configuration so that's what I did.
I've used batteries from Chrome Battery in the past and am very happy with them.
https://www.chromebattery.com/ytz7s-...s-battery.html