In what was one of the worst kept secrets in automotive news, Tesla announced today that it's releasing a 100-kwh battery pack for the Tesla Model S and Model X. The new P100D models will sit at the top of the Tesla range, giving the Model S 315 miles of all-electric range and thereby making it the first EV to top the 300-mile mark.

The Model X P100D will have a range of 289 miles. Tesla is claiming that the Model S P100D with Ludicrous mode will be the quickest accelerating production car - if you don't count the Porsche 918 or Ferrari LaFerrari - in the world with a 0-60 mph time of 2.5 seconds. There's no word on horsepower quite yet.

The Model S P100D will start at $134,500 and the Model X 100D will start at $135,500, but Model S and Model X P90D owners can upgrade their battery packs for $20,000. If an owner has already ordered a P90D but hasn't taken delivery, they can spend an extra $10,000 for the extra power and range. Tesla says the extra $10,000 goes to recycling the old battery pack.

"This has been a very difficult development," Musk said to reporters, "going from roughly 90 to 100" was "more like a 50-percent increase in difficulty." He also said that the battery's complexity will lead to low production numbers.

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