The Diegard, Interstate and Costco brands are all manufactured by
Johnson Controls (and are pretty good batteries). Their web site
used to list all the brands they supply but it no longer does (it
does have some good basic info on auto batteries, though). Note
that they are not the only Sears supplier so other battery Sears
"models" might be from different suppliers.

There are two sizes. The smaller size is what comes from the factory.
A slightly larger battery is available that fills the entire battery tray.
Downside to the larger battery would be more weight. I went with the
smaller size since I live in a mild climate and the low compression
turbo engine (I have a T5) seems to be pretty easy to crank.
(I suspect you also live in a mild climate if you still have the original
battery since they rarely make it past 4 years.)

I'd also check the battery ground lead where it grounds to the vehicle.
A bad or corroding ground connection will cause odd electrical problems.