Tesla Roadster is being upgraded to extend its range to 400 miles

Tesla's new Model D may be the hottest electric car around, but the company revealed today that you shouldn't discount its older Roadster just yet.Tesla CEO Elon Musk tweeted on Christmas that the Tesla Roadster will be upgraded to "enable non-stop travel from LA to SF - almost 400 mile range," promising more details today.Those details, delivered in a Tesla blog post, explain exactly what the Roadster 3.0 upgrade will entail: a new battery cell with 31% more energy, a retrofit aerodyn