For National Plug-In Day this year, the third time was definitely the charm.

In its third year, the weekend celebration of automotive electrification included events in more than 100 cities--up from 65 last year--on both September 28 and 29.

It also became an international event, with cities in Canada, Mexico, and the Netherlands participating as well as those in the United States.

Tens of thousands of attendees collectively test-drove every new electric vehicle on the market, from the Tesla Model S to the Brammo electric motorcycle, and learned more about this alternative form of propulsion.

Electric-car owners (there are now more than 100,000 in the U.S.) also got the message across with "Oil-Free Miles" placards displayed on windshields, showing how many miles their cars had been driven without an oil change.

In many cases, that meant every mile the car had covered.

Here's a brief roundup of just a few of the many events that happened over the weekend.

NASHVILLE

Nissan decided to promote electric cars by giving out free gasoline.

Free gasoline as bait, that is.

As drivers filled up their internal-combustion cars, Nissan representatives explained how much money they could potentially save by switching to electricity.

In addition to taking over a gas station in Nashville--not that far from where the Leaf electric car is built--Nissan gave out free gas at stations in Atlanta, Los Angeles, and San Francisco.

National Plug-In Day 2013: Students show off converted Volkswagen Beetle electric car.

National Plug-In Day 2013: Students show off converted Volkswagen Beetle electric car.

LONG BEACH, CALIFORNIA

More than 245 electric cars descended upon this Southern California city, but one of them was not like the others.

"Volts Wattson," a 1971 Volkswagen Super Beetle convertible, had been converted to electric power by a group of high-school students.

The students--aged 14 to 18--removed the car's gasoline engine, replacing it with an electric motor and a 30-kilowatt-hour lithium-ion battery pack. They claim a range of 100 miles or more for their creation.

SACRAMENTO

About 4,000 people and 50 cars on display celebrated National Plug-In Day in Sacramento.

Organizers conducted more than 250 test drives, covering 700 miles and giving many attendees their first-ever chance to drive an electric car.

A brand-new 2013 Tesla Model S was among the vehicles on offer, and proved very popular.

More than 10 Model S cars--plus a few Tesla Roadsters as well--were arrayed around one of the first Tesla Supercharger stations near the Folsom Outlet Mall, in what became known during the event as "Tesla Alley."

Elsewhere in the state capital, Governor Jerry Brown marked National Plug-In Day by signing six bills that help promote electric cars.

National Plug-In Day 2013: Electric cars on the National Mall [Photo by Eric Cardwell].

National Plug-In Day 2013: Electric cars on the National Mall [Photo by Eric Cardwell].

OTHER CITIES

Cities from Maine to Hawaii hosted events, and many saw large boosts in attendance compared to last year's events.

Dozens of electric cars lined the National Mall in Washington, D.C., stretching from Pennsylvania Avenue to Independence Avenue.

An estimated 2,000 visitors attended the Plug-In Day event in Cupertino, California, and Orlando saw about 1,000.

And the list goes on...

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