"The more powerful your battery, generally the more dangerous/flammable/explosive it is when it fails." No, that's not really a thing at all. Li-ion batteries

"The more powerful your battery, generally the more dangerous/flammable/explosive it is when it fails." No, that's not really a thing at all. Li-ion batteries burn because they contain a combustable electrolyte. The initial explosive reaction doesn't have that much to do with the energy in the batteries. The long term reaction is related to the energy in the battery, but only because the electrolyte burned off letting the anode and cathode short out. There are plenty of demonstrations of solid state li-ion batteries that have way higher power density, but that can be cut in two without any explosive reaction at all. The challenge with most of these is cycle life btw. In the extreme case, you can get insanely high energy density out of aluminum-air batteries, but as far as I know they're perfectly safe. Making a safe battery with high energy density is easy. Getting all the other parameters right is hard.