That's my point. If its a decent battery, then WHO you buy it from can be as important or more so, than what battery you are buying. Costco has always proven to be a great company to deal with as far was warranty.
BTW, Interstate doesn't manufacture a battery. They provide batteries under private labels and warranty them. But they only distribute batteries like 90% of the others out there with their name on a battery.

But with Costco, you have kind of a double whammey warranty, with Costco backing it, as well as Interstate. Both whos entire reputation is built around their products and customer service.