Starbucks is offering wireless phone charging via Duracell Powermat. The chain has chosen 17 locations around the Boston area for a "limited time in-store trial for wireless charging," according to Starbucks chief digital officer Adam Brotman. "We're building the Powermat technology into some of the tabletops, just to get a sense for how our customers will react, compared to having to plug their mobile devices into the wall."