Electric cars are still such a novelty that little is known about their owners and how they use the vehicles. But recent research is beginning to unlock some of the mysteries.

Plug-in vehicles—those that run entirely on battery power or that combine electric and gasoline drives—represent less than 1% of total U.S. vehicle sales, but in the past three years their numbers have grown rapidly. Sales nearly tripled in 2012 and are on track to nearly double this year, according to the Electric Drive Transportation Association,...