The jury is still out on whether people will be willing to pay the upfront cost for a stationary battery or at least lease one for the promise of a potential reduction in electric bills by 20 percent to 30 percent. SolarCity, which names Musk as its chairman and recently expanded into Reno, says it has installed 300 Tesla storage batteries in the Bay Area for its Battery Storage pilot program, with 150 more expected to be added early this year. One customer is David Cunningham, an aerospace engineer from Foster City, Calif., who paid $7,500 for the battery after state incentives reduced the $18,300 sticker price.