The Japan New Energy and Industrial Technology Development Organisation (NEDO) has developed a battery/electric "hi-tram". This is described as a contact wire/battery hybrid Light Rapid Transit (LRT) vehicle in Railway Technology Avalanche (19 September 2008). There is no internal combustion engine (as in a hybrid car); instead the battery is recharged from the overhead wires. The tram can then lower the pantograph and run on battery power for a few km. This allows trams to be used in places where overhead wires cannot be installed for cost, safety or aesthetic reasons. There is a video of the tram in operation.
The vehicle is also referred to as a "Contactwire-less Tramcar" and uses Lithium Ion batteries. Obviously it would be feasable to create a hybrid trolleybus, using similar batteries and motors to the tram. This would be able to drive on unmodified roads on battery power and then recharge when on main routes equipped with overhead wires.