T. Ikeya, N. Sawada, J. Murakami, K. Kobayashi, M. Hattori, N. Murotani, S. Ujiie, K. Kajiyama, H. Nasu, H. Narisoko, Y. Tomaki, K. Adachi, Y. Mita, K. Ishihara, "Multi-step constant-current charging method for an electric vehicle nickel/metal hydride battery with high-energy efficiency and long cycle life," J. Power Sources, vol. 105, no. 1, pp. 6-12,Mar. 2002.