As predicted last month, and tweeted and teased by CEO Elon Musk, Tesla Motors showed off battery swapping for its Model S electric car at a press event last night.

Held at Tesla's design studio in Hawthorne, California, the demonstration itself was simple: A Tesla Model S drove onto the stage and stopped over a hole in the floor.

Automated arms reached through the hole, supported the pack and the car, disconnected the fittings, and dropped it through the hole.

Then a replacement pack was moved into position, raised through the hole to sit under the car's floorpan, and reconnected to the car.

The entire process took roughly 90 seconds. The driver remained in the Model S throughout, and pulled away at the 1:33 mark.

Meanwhile, a countdown clock on the video screen behind the car showed a Tesla employee filling an Audi A8 with gasoline at what Musk claimed to be "the fastest gas station in L.A."

Enthusiastic owners

After Musk apologized for the length of time required to fuel up the Audi, the enthusiastic crowd of several hundred--largely Tesla owners--laughed when a second Model S drove on stage.

It too had its battery pack swapped from underneath, and managed to drive away before the Audi finished fueling after more than 4 minutes.

If you want another view of the events beside Tesla's promotional video shown above, try this one.

As Musk has noted, the Tesla Model S was designed from the start to enable its battery pack to be quickly and easily swapped out.

Once the flashy part was over, Musk turned his attention to the details. Our brief summary:

TIMING + LOCATION

Tesla will roll out battery-swapping in California first, with the San Francisco-Los Angeles corridor along I-5 going live by the end of this year

Then sometime next year, the company will turn its sights to the Northeast Corridor from Boston through New York City to Washington, D.C.

"Tesla Stations" that offer swapping will be located in the same sites as Supercharger fast-charging stations

Each will have about 50 batteries, which will be kept fully charged by the existing infrastructure for charging energy-storage batteries at those sites

"FAST" vs "FREE": RELATION TO SUPERCHARGING

The Supercharger network of DC fast-charging stations will remain, and it will continue to be free for Model S owners to use

For the much faster swapping, Tesla will charge owners a fee for the fully-charged battery pack swapped into their car

That fee will be roughly equivalent to the cost of 15 gallons of gas, Musk said, perhaps $60 in California

In other words, a 20- to 30-minute Supercharge to recharge a pack to 80 percent will be free, but a full recharge in 90 seconds will cost the same as a fill-up

Photo of Tesla Model S battery swapping versus 'fastest gas pump in LA' tweeted by Elon Musk

NEW vs ORIGINAL PACKS

Tesla expects that many owners will return to the same station and have their original pack swapped back into their car on the return leg of their journey (for another fee)

Otherwise, owners can have their original pack returned and swapped into their car later for a "transport fee" that hasn't been set yet

Or, if owners elect to keep the pack they received in the swap, Tesla will bill them if that pack is newer than the original that was swapped out

The supply of swappable packs will all initially be brand-new, but Musk noted that over time, they will age--meaning the swapped-in pack could vary in its energy capacity

A 60-kWh Model S could indeed have an 85-kWh pack swapped in, but unless it's returned, the owner will pay a major upgrade fee

FUTURE OF PACK SWAPPING

According to Musk, the swapping stations, at $500,000 each, are a way to make electric cars fully compatible with gasoline cars in range and "refueling time"

He suggested that in crowded cities like London, swapping stations might prove more space-efficient than the space required for multiple cars to park and recharge

He also hinted that third-party companies might come into the picture to provide swapping stations in some locations

Looking ahead to the company's third-generation electric car in 2016, Musk wasn't convinced that swapping would remain relevant as batteries and charging improved

The event was covered by media outlets that included Forbes, GigaOm, TheVerge, and many others.

What's your take on Tesla's announcement? How important is battery swapping to the future of electric cars?

Leave us your thoughts in the Comments below.

[hat tip for YouTube video: Brian Henderson]

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