Europe is seeing the commissioning of a new class of locomotives. The electric-battery locomotives. Yes, it sounds weird, but these locomotives use overhead traction for travelling on electrified lines and onboard batteries for non-electrified lines. These locomotives are quickly replacing the diesel locomotives which were in vogue on partially electrified lines.
Stadler of Switzerland will be supplying Seven Geaf 2/2 shunting locomotives to Rhätische Bahn. Of these, two have been delivered. The locomotives are for use on the meter gauge. These locomotives would primarily use the overhead traction for normal operation. However, they carry an auxiliary lithium-ion battery pack which provides power when the electrification is switched off or when operating on non-electrified tracks.
The auxiliary Li-ion battery pack has replaced the auxiliary diesel engines installed on the previous generation locomotives.
The locos are rated at 500 kW and have a maximum speed of 80 km/h when using overhead electric supply. When on batteries, the speed is limited to 40 km/h and power to 200 kW.
The Transport Journal 