Obviously, unless we manage to somehow get usable sea-water based batteries, any mass-market battery technology will have a tremendous impact on the environment

Obviously, unless we manage to somehow get usable sea-water based batteries, any mass-market battery technology will have a tremendous impact on the environment. The problem is not manganese or lithium, it is the mass production and consumption, unregulated vehicle growth (in size and weight), all of this encouraged by pro-cars regulations, the US being the worst offender.