I used to work as a mechanic right next to a business called "Battery Warehouse". They had pallets of unmarked batteries on the floor that had no labels on them. All of the labels were on the wall, and they slapped whatever label on the battery that you requested. That was 40 years ago, but I was told then that there were only three manufacturers of batteries in the country.
I don't know for sure, but I wouldn't be surprised if that is still how most of the batteries are sold.