Right now, there is roughly one public charger for every 10 electric vehicles — about 15,000 in California and 33,000 across the country, according to ChargePoint, one of the biggest charging-station companies. (There are thousands of other, unofficial charging spots that are essentially wall outlets that businesses or homeowners have made available for public plug-in).

The larger public charging stations tend to look like high-tech gas pumps and often are in parking lots. But they can vary widely in cost and charging power. Some take half an hour for a charge and others four hours or more; many are free or subsidized, and others cost $1 an hour or more. Public charging stations and lights on many vehicles indicate when a car battery is full.

Most people charge at home (using an electrical outlet) but also want to use public chargers, in part because the cars have a limited range — typically 80 miles. On top of this “range anxiety,” as it is called, drivers like the idea of getting a free or low-cost charge at a public station.

“Imagine going to a gas station that says, ‘Here’s free gas.’ Who wouldn’t want to muscle in and say, ‘I’ll take some free gas’?” said Ollie Danner, the founder of EVPerks, a California company that works with local and national businesses to offer coupons and other incentives to electric vehicle drivers.

The rudeness is not just among drivers of electric cars. By many accounts, owners of gas-powered cars often take up desirable parking and charging spots that companies and cities reserve for electric cars. This habit has inspired the spread of a nickname: ICE Holes. (ICE stands for internal combustion engine.)

“Some people say, ‘I just wish I could key their cars,’ ” said Jack Brown, who created the EV Etiquette Survival Packs and a Facebook page devoted to complaining about the interlopers.

Image Mr. Brown's EV Etiquette Survival Pack. For $15.99, a pack includes hang tags for vehicles that urge fellow drivers not to unplug others’ cars while charging. Credit... Jason Henry for The New York Times

Mr. Brown, who works in Google’s driverless car division and used to work at Tesla, includes in his survival packs a notice to put on gasoline-engine cars. It reads, “EV charging spaces are functional reserve spaces, just like disabled drivers spaces.” The tag goes on to say that blocking the spaces “is not only inconsiderate, it is illegal in many areas.” But it also includes stickers that inform other drivers that it is all right to unplug a car if it is fully charged, and others that ask, “Can you plug me in when you’re done?”