Neither manufacturer names the other. One publishes what the device requires, the other publishes what the battery does, and we have set the two side by side — including wherever they do not meet.
Winnebago specify “2 deep-cycle Group 31 batteries AGM maintenance-free” for this floorplan. Interstate state this pack is “Group Size 31T” and an AGM. BOTH ARE NAMING THE SAME BCI GROUP, which is a dimensional standard — 330 x 173 x 240 mm — rather than a measurement either of them took. A pack that is a Group 31 fits a Group 31 space by definition of the standard, so the size question here is settled rather than estimated. Interstate also describe it as a 2-in-1 doing cranking and deep-cycle duty, so it is a candidate for a starting battery elsewhere as well, and Winnebago ask for deep-cycle here.
Only the house bank, and Winnebago fit TWO of them — this is not the chassis starting battery — check yours before buying.
Two of these.
Not established: which terminal type the van expects. Group 31 comes as 31T with top posts and 31A with threaded studs, and the two share an envelope — so a pack of the right SIZE can still have the wrong POSTS for the cabling. Winnebago do not state which their trays are wired for, and this pack is a 31T. Check the terminals before buying.