Abstract: The present invention relates to a method for converting a diesel-electric, or diesel hydraulic rail vehicle to an all-electric rail vehicle capable of moving on partially electrified railway tracks, comprising providing the vehicle a storage and autonomous supply electric power system comprising an electric traction unit, if not present in the vehicle prior to the conversion, or if the existing electric traction unit is to be replaced; an accumulator unit comprising one or more electricity accumulators, and a super capacitor unit comprising one or more super-capacitive assemblies; a power supply device for supplying external power when available to the traction and the storage and supply system, and a control and distribution system for distributing electric power between the traction system, the power supply device and the electric power storage and autonomous supply system according to the traction operation and availability of external power.