There was an article from some car magazine I read a while back. They did some battery testing, Walmart included. They found out what I had suspected but didn't ever want to tell anyone because I figured folks would think I was a nut job. And I honestly thought I was imagining things and just chalked it up to luck. It doesn't really make a lot of sense but, one companies batteries of a specific group size can be MUCH higher or lower quality on average than their other group sizes in the same line/cost level. I don't remember the group size I use in my F350 but, I use the next size up from what's required. They are a tight fit but they last for years in my trucks. The last I replaced was over 8 years old. The "proper" size hasn't lasted over 4 years in any F350 I know of. Remember, this is Illinois, we beat batteries like they are rented mules up here during the winter.
I wish I knew what article it was, the guys doing the testing were baffled as to why there was such a difference. I wonder if the different group sizes are sourced from different companies or something. That could be the thing that would explain the quality differences.
Hahaha, and don't be so hard on yourself! Batteries are one of those items everyone has an opinion about, just like oil brand/viscosity etc.