thanks for the heads up and kudos to TJM
it could have been a bad day on the robot welder, or there is a lack of welding in this area of the tub on the mazda, don't matter but I'm now wary?
I was thinking that this location was perfect on my dual cab, in fact have mounted a portable battery in this location, strapped down.
why strapped down- well I stuffed a "thumper battery box" in the rear of the dual cab when not held down, quite a lot of pendulum forces in the rear of a dual cab behind the axle.
lesson learnt and further gained from this thread, especially as I was looking at a 150ah battery
have to rethink the design and placement of the battery tray