Rare Tesla factory tour reveals new laptop batteries pack

On Wednesday, Tesla gave journalists a rare tour of its Palo Alto headquarters and a first-ever glimpse of the battery pack that will power the upcoming Model S sedan. While the battery pack for Tesla's Roadster is essentially a large box containing thousands of individual battery cells, the Model S battery pack is flatter and nearly the width and length of the car. "The Model S battery is perfectly flat," said Peter Rawlinson, vice president and chief engineer for vehicle engineering. For the Roadster, Tesla strung together nearly 7,000 laptop batteries into one battery pack. Practically every company that makes a lithium-ion battery has sent its cells to Tesla, which puts them through rigorous testing, with a focus on extending their life and safety. A key metric for batteries is "energy density," which refers to the acceleration and range the batteries can provide. Tesla claims the energy density of the Model S battery pack will exceed 135 watt-hours per kilogram. The Model S, which will be capable of going from 0 to 60 mph in 5.6 seconds, will come with a choice of three battery packs, capable of ranges of 160, 230 or 300 miles.