Roadster upgrade will enable non-stop travel from LA to SF -- almost 400 mile range. Details tmrw. Merry Christmas! - Elon Musk (@elonmusk) December 25, 2014

Update: Tesla has just spilled the beans on the update, and it seems the Roadster isn't just getting a new battery. The company's first-ever production vehicle is instead being furnished with a "Roadster 3.0" upgrade package that consists of the previously announced battery upgrade, an aerodynamics kit and improved tires. The aerodynamics kit improves the Roadster's drag by 15 percent, which will improve fuel efficiency. The new tires offer a 20 percent improvement in "rolling resistance," improving fuel efficiency further. Tesla says it's also making improvements to the wheel bearings and brake drag, which when combined with the other additions will improve range by 40 to 50 percent, giving the Roadster a 400-mile-plus range.

There's no word on when the 3.0 upgrade will be released -- or how much it'll cost -- and the package is currently described as a prototype. Tesla will demo the improvements in early 2015 by driving non-stop from San Francisco to Los Angeles, and says the upgrade won't be the last offered to owners of the now-discontinued Roadster.

Aaron Souppouris contributed to this report.