Rubber tyred gantry (RTG) cranes are an important piece of transport equipment in ship and rail container terminals. They have a diversified power demand, for example, peak powers of 292-kW driving, 178 kW regenerating, and 7-kW idle power. The high peak power demand determines the system prime mover (internal combustion engine) rating, which is highly over-rated for the crane average energy requirements. Such a variation in peak to idle power demand favors a hybrid power solution which, given appropriate design, can yield significant gains in fuel or energy usage and, importantly, reductions in local emissions, thus improving air-quality. In this study, a hybrid energy source for an RTG crane is presented. The hybrid energy source comprises of a lithium battery and a down-sized diesel-generator connected to the dc link through an active front end unit. While other systems have been previously proposed, the system presented here utilizes a smaller diesel-generator, thus reducing plant and fuel consumption. In addition, the battery connects directly to the dc link reducing system power electronics while improving battery response and efficiency. Experimental results from a full-size evaluation system are presented showing a 57% reduction of fuel consumption compared to a conventional RTG crane system.