FWIW, I have never, ever seen a Group 31 battery, either starting or otherwise, in any Wal-Mart (and I've been in hundreds all across the country). I have seen them in Sam's Club, but that does me no good since I'm not a member there. The last time I bought starting batteries at Wal-Mart (to replace, I am not kidding, a pair of 8D's), I have to settle for Group 65 as the largest batteries they had in stock.
To echo Sojourner's comments, it behooves you to read up and learn about the differences between battery types. Talking about "adjustments" under warranty suggests you are looking at starting batteries, which are unsuitable in any case for house batteries. Deep-cycle batteries are warranted the same way your TV is -- you need to send them back to the manufacturer, who will make a determination why they failed and decide what sort of compensation, if any, you might be entitled to. In general, you can go to any distributor for the brand you own to start the warranty process -- it should not matter where you actually bought them.
The concept of bringing the battery back to the store (after it has been used) and getting either a free replacement or a credit towards a new battery, no questions asked, is a concept limited entirely to the highly competitive automotive starting battery market. And, BTW, you will note that heavy-duty sizes such as 8D, 4D, and sometimes even Group 31, do not qualify for this type of warranty even in the stores and brand names that usually offer it.
You may want to read this topic:
http://www.busconversions.com/bbs/index.php?topic=4329.0Lots of good discussion there, and do check out the other link I posted in that topic (in addition to the same one Sojourner posted):
http://www.phrannie.org/battery.htmlHTH.
-Sean
http://OurOdyssey.BlogSpot.com