The Holy Grail for electric vehicles is to someday be able to wirelessly re-charge batteries on the fly, rather than having to stop, plug in and wait hours before hitting the road again.

Wireless charging on the go is still an unproven technology. But last week, San Diego's Qualcomm demonstrated its vision of dynamic electric vehicle charging on a test track in France, showcasing that progress is being made toward recharging while in motion.

Using its Qualcomm Halo wireless electric vehicle charging system, the San Diego company said it charged Renault Kangoo electric vehicles on a 100-meter test track at highway speeds, delivering 20 kilowatts of power along a track.

That's hefty power that could fill batteries fast. Most in-home, plug-in electric vehicle charging systems deliver 3.3 kilowatts to 6.6 kilowatts. They typically take hours to fully recharge electric vehicles.

Qualcomm didn't reveal what percentage of power was lost in the wireless transfer or other performance details of the demonstration. But it did say two vehicles on the same track can charge at the same time, and vehicles can pick up a charge in both directions.

Additional testing will be performed by Vedecom, a public/private partnership of the Institute for Energy Transition, which was created by the French government to advance "carbon free and sustainable mobility."

Vedecom members include firms in automotive, aviation and technology, as well as academic institutions. It aims to determine the feasibility of dynamic electric vehicle charging.

One hurdle could be the expense. The 100 meter test track used in last week's demonstration costs $10.1 million, which was funded mostly by the European Commission. It included Qualcomm's Halo wireless charging equipment installed in the roadway that syncs with receiving plates in the vehicles to recharge batteries on the go.

Others are working on dynamic charging, too. Last year, a 20 kilowatt wireless charging system was demonstrated at the U.S. Department of Energy's Oak Ridge National Laboratory in Tennessee.

Omer Onar, a fellow at the Oak Ridge National Lab, said at the time that dynamic charging is important because it can reduce batteries required in an electric vehicle, which are among its most expensive components.

And dynamic charging technology doesn't have to be installed along every mile or roadway. Shuttle buses and other vehicles with defined routes can potentially receive enough of a wireless charge while stopped to make it to the next charging station along their route, he said.