Honolulu-based Volta Industries LLC has expanded its free-to-use electric vehicle charging businesss to Arizona.

Volta is now offering EV charging at 12 charging stations located at shopping centers in Phoenix and Tucson.

The company’s goal is to have 500 charging stations across the U.S. by the end of 2014, according to Arden Penton, Volta’s director of media and operations.

The company uses a business model in which EV owners are able to hook up to a Volta charging station at no cost. The service is paid for through advertising on the charging kiosks. Volta generally places the charging stations in locations with high visibility, such as shopping malls.