 It was commercialized in Sweden in 1910 and reached the United States in 1946.The first models were robust and had significantly better energy density than lead-acid batteries, but were much more expensive.Waldemar Jungner patented a nickel–iron battery in 1899, the same year as his Ni-Cad battery patent, but found it to be inferior to its cadmium counterpart and, as a consequence, never bothered developing it.