Battery-powered cars will begin appearing soon in driveways of consumers, but electric vehicles already are gaining early traction in another realm: commercial delivery fleets. Staples Inc., the Frito-Lay, FedEx Corp., AT&T Inc. and a few other companies have begun purchasing electric delivery trucks. Proponents say they make more sense in many ways than electric cars. That’s because delivery trucks generally drive short, defined routes each day, which are better suited to the limited range of battery power.