Batteries also come in different amperage and battery shelf life. What you get at Walmart is the lowest grade of batteries.
I used to think so too (I was an auto tech in a previous life) until I realized that Johnson Controls makes Walmart batteries.
"Major OEMs and aftermarket retailers include Daimler, General Motors, BMW, Ford, Toyota, Hyundai, Kia, Volkswagen, SAIC, Bosch, Walmart, Halfords, Interstate Battery System of America, Advance Auto Parts, AutoZone and Sears."
http://www.johnsoncontrols.com/publ...a_kit/about_power_solutions/backgrounder.html
I doubt it makes much difference what brand of battery you buy from these guys...all are pretty good. Just check the warranty, though since they are pro-rated, I'm not sure how much difference that makes either. Just make sure you're comparing apples to apples when it comes to amp hour size ratings. Quality wise, you'd have to ask them if they have different standards for the different branded batteries they market. When it comes to true deep cycle fork lift and solar storage batteries, that's a whole other animal, though.