This is the important point. A whole lot of things are dangerous when you're using them. But when you're not they're largely safe. Various saws, tools, cans

This is the important point. A whole lot of things are dangerous when you're using them. But when you're not they're largely safe. Various saws, tools, cans of gasoline, propane, butane, etc. They're all unlikely to be used on a 'set and forget' kind of basis. Whereas a battery bank is VERY likely to be used that way. Set it up and get on with other activities, likely including leaving the building entirely. Meanwhile the unsupervised device has an exponentially greater risk of become unstable and causing tremendous damage. It seems like a clever idea but how much risk it poses is debatable. One would hope anyone attempting to do this is going to be dissuaded from pursuing it on a grand scale because of the various problems they're going to have along the way. But some 'mad scientist' types are never going to be dissuaded. With luck the rest of us will at least get an entertaining video clip of their disaster. Hopefully without anyone else suffering from the ignorance.