The primary battery 10mm no problem but secondary battery the setup is different and not sure how to get it off. tried with 3/8 socket no luck 10mm. Pliers was able to loosen nut on positive but not negative
Removing the positive cable works too, you just have to be careful. But the vehicle should be dead with just the primary ground disconnected.
When you're removing the ground wire, it doesn't matter if you touch anything else metal with your tool/socket.
When you're removing the positive wire, if you touch any other metal, you might create a short and bad things tend to happen.