In 2003, the world's biggest battery was connected to provide emergency power to Fairbanks, Alaska's second-largest city. Without power lines between Alaska and the rest of the U.S., the state is an "electrical island." Worse, tough environmental conditions cause a total city blackout every two or three years. The $35 million rechargable battery contains 13,760 large nickel-cadmium cells that weigh a total of 1,300 tonnes and cover 2,000 square metres, an area greater than a sports field. The battery can provide 40 megawatts of power, enough for around 12,000 people, for up to seven minutes, while diesel backup generators are started. This will be an important safeguard, where winter temperatures can drop as low as -51ºC.