They used to be made by Exide here, but they've switched to Johnson Controls as of about July. A press release by Johnson Controls says that they are now the sole supplier to Wal-Mart for car batteries.
The only problem with Walmart Everstart Maxx batteries is the warranty is 3 years free replacement, no more 8-9 pro-rate. While the others have 2-3 years free replacement plus some pro-rate up to 8-9 years.
My 2 Walmart's both have 3 year free replacement posted at the top of the shelf of the Maxx batteries. Asked them, they said the battery manufacture (Johnson Controls) drops the pro-rate to keep the price low.