A deal to provide a mechanical system for 20 delivery trucks is about to put Eaton Corp.'s diesel-electric hybrid technology to the test, according to a report in the Associated Press. At stake is the potential for the Cleveland-based industrial technology corporation to eventually power a FedEx Express fleet of 30,000 medium-size delivery trucks. Meanwhile, FedEx Corp., based in Memphis, Tenn., sees a way to cut fuel cost by as much as 50 percent. Environmental Defense, a New York-based organization that coordinated the deal in partnership with FedEx, anticipates fuel conservation and cleaner air. On-the-road testing of the FedEx OptiFleet E700 hybrid delivery trucks is to start in January. The trucks will be based in four cities. FedEx has not disclosed the locations. Hybrid technology — which also has been tried on a small scale by FedEx rival UPS — offers potential for substantial growth in Eaton's $1.2 billion truck division, now smallest among the company's four segments. The other divisions are automotive, fluid power and electrical. The Eaton hybrid is a diesel engine equipped with filters to limit emissions, working in combination with an electric motor linked to a battery. The computer-controlled system saves the driver from deciding when to switch between diesel or electric power.