For anyone needing to replace their battery, here's what I just did:
My Cobalt SS/SC came with a T5 size battery, when I originally installed it I left the J-bolts as long as I could for future changes if needed. My flooded lead-acid battery decided to start leaking a couple days ago and dripping onto my frame and garage floor.
I decided to go with an AGM style to avoid the possibility of leaking in the future and to not make the front end even lighter, problem is that it seams the T5 size isn't used for AGMs (or I just didn't find it). I did find that H5 size batteries (also known as group 47) have the same footprint and are just 5/8"-3/4" taller depending on the exact model.
I picked up an Interstate Batteries MTX 47/H5 and just installed it yesterday. Was able to pick it up from the local auto shop 3 miles from home after they ordered, price isn't the lowest but still just $209+tax so not too far above typical flooded lead-acid batteries depending on size. I also updated my wire connectors from the hack job someone did when it was in the cobalt which included the clamping style connectors that got loose when I was in Charlotte the other year. I now have soldered/crimped with glue style heat shrink sleeves that bolt onto the terminal clamps, hopefully they will be nice and trouble free. Since I didn't want to fully remove the positive starter cable from the car to solder the new end on, I just torched the lug in the empty battery space, that was a little odd but worked just fine. Red electrical tape to cover the exposed bolt area of this style connector to prevent accidental shorting.
So I originally had a T5 size battery, swapped that for an H5/group 47 size AGM battery and it seems to fit very nicely. They have the same footprint and the H5 is just a little taller but fits just fine if you left the hold down bracket bolts a little longer.