Elon Musk suggests a Tesla trailer with a booster battery for long distance driving.

Elon Musk was at least a tad bleary-eyed. On his way back from Hong Kong to Tesla’s headquarters in Palo Alto, California, Musk stopped by Tesla Paris to greet a packed room of Tesla fans. The Parisian Tesla enthusiasts had some tough questions for Musk. Many in the room wanted a Tesla car that could travel 800 to 850 kilometers (500 miles) on a single, fully charged battery. Musk told the audience that improvements in battery range are coming. By next year, Musk foresees a Tesla battery range of of 500 kilometers (300 miles). Musk has previously stated that Tesla battery capacity should increase roughly 5 percent per year when Tesla’s “Gigafactory” gets up and running.

Here’s where things got really interesting.

Then Musk threw out an idea that’s been talked about among Tesla fans, but never endorsed by anyone involved with Tesla itself. “What if you had a trailer with a booster battery that you could use for long distance driving?” suggested Musk. Musk qualified his suggestion by informing the audience that he had only one hour of sleep over the past 48 hours of globe-trotting. Nevertheless, a tag-along trailer with an auxiliary battery makes sense to many Tesla observers and enthusiasts.

The entire appearance is well worth a watch.

As for a single, 500-mile battery, the technology and practicality for such a battery just isn’t quite there yet. A 500-mile battery currently would be too heavy and too expensive for a Tesla car. Unless and until Tesla develops innovative ways to get more out of the batteries that it will produce, the 300-mile battery is the gold standard.The Q&A portion of Musk’s appearance in Paris begins at the 11-minute mark.