Lithium-ion batteries provide higher charging efficiency and no memory effect, giving them an advantage over nickel-hydrogen batteries. With such excellent characteristics, the lithium-ion batteries are considered to be the most likely power source for HEVs FCEVs and so on. In 1999, we developed lithium-ion batteries featuring long service life, high output, high energy density, and high reliability, and delivered them to HEV. It has been adopted as the battery for eco-friendly cars by its distinct features for better charging efficiency than the Nickel metal hydride battery and memory-effect-free performance. In actual application for vehicles,many cells need to be combined as a module to form a battery pack with additional control circuit to monitor voltage or temperature for safety use. Moreover reliability under severe conditions and high safety level in case of crash or accident is required. The Hitachi's R&D Group is developing battery of "long operating life", "high power", "high energy density", "high durability", "safety", and "low cost" for automotive applications. These batteries are now widely used in hybrid electric small-sized trucks, buses and hybrid railway motorcars.