An auxiliary converter adapted to provide power to auxiliary loads of an auxiliary electrical network of a railway vehicle, the auxiliary loads including a main air compressor, the auxiliary converter comprising: - a main inverter stage with a main inverter input and a main inverter output, the main inverter stage being configured for generating an AC voltage at its main inverter output from DC voltage received at its main inverter input from a live catenary; - a transformer stage connected to the main inverter output and adapted to convert, in a catenary operating mode, the AC voltage from the main inverter stage, the transformer stage having a supply output for supplying a supply voltage to the auxiliary loads and a separate charging output for supplying a reversible battery charger; and - the reversible battery charger being connected to said charging output and adapted to charge, in said catenary operating mode, an electrical battery of said railway vehicle, wherein the reversible battery charger is adapted to, in a battery operating mode, deliver a supply voltage from the battery to said transformer stage for powering auxiliary loads, characterised by a high power rectifying and inverting stage connected to said supply output and adapted to provide power to said auxiliary loads of said auxiliary electrical network, wherein said high power rectifying and inverting stage comprises in series from input to output a single phase rectifier, a set of buffer capacitors and a three phase inverter. - a main inverter stage with a main inverter input and a main inverter output, the main inverter stage being configured for generating an AC voltage at its main inverter output from DC voltage received at its main inverter input from a live catenary; - a transformer stage connected to the main inverter output and adapted to convert, in a catenary operating mode, the AC voltage from the main inverter stage, the transformer stage having a supply output for supplying a supply voltage to the auxiliary loads and a separate charging output for supplying a reversible battery charger; and - the reversible battery charger being connected to said charging output and adapted to charge, in said catenary operating mode, an electrical battery of said railway vehicle, wherein the reversible battery charger is adapted to, in a battery operating mode, deliver a supply voltage from the battery to said transformer stage for powering auxiliary loads, characterised by a high power rectifying and inverting stage connected to said supply output and adapted to provide power to said auxiliary loads of said auxiliary electrical network, wherein said high power rectifying and inverting stage comprises in series from input to output a single phase rectifier, a set of buffer capacitors and a three phase inverter. wherein the reversible battery charger is adapted to, in a battery operating mode, deliver a supply voltage from the battery to said transformer stage for powering auxiliary loads, characterised by a high power rectifying and inverting stage connected to said supply output and adapted to provide power to said auxiliary loads of said auxiliary electrical network, wherein said high power rectifying and inverting stage comprises in series from input to output a single phase rectifier, a set of buffer capacitors and a three phase inverter.