The traction battery of the first generation Prius update (2000 onwards) was a sealed 38-module nickel metal hydride (NiMH) battery pack providing 273.6 volt, 6.5 Ah capacity and weighing 53 kilograms and is supplied by Japan's Panasonic EV Energy Co. They are normally charged between 40–60% of maximum capacity to prolong battery life as well as allow headroom for regenerative braking.