A method for powering emergency auxiliary loads in a railway vehicle from a rechargeable electrical energy storage device on board the railway vehicle capable of storing a quantity of energy sufficient to allow the emergency auxiliary loads to operate in emergency mode for at least some thirty minutes from that single source of energy, the method comprising a normal mode in which a charger charges the electrical energy storage device, this charger being capable of producing a rectified DC voltage through which the electrical energy storage device can be charged from a three-phase voltage in normal mode obtained from electrical power captured from a catenary, this charger comprising: • three input terminals each connected to one of the phases of the three-phase voltage, • two output terminals (106, 108) connected to the electrical energy storage device to which the rectified DC voltage is delivered, • three arms connected in parallel between the two output terminals, each arm comprising two controllable switches (I H, I B) connected in series through a mid-point, each mid-point being connected to a corresponding input terminal, • a unit controlling switching of the switches to rectify the three-phase voltage, characterised in that the method comprises steps in which: - a controllable power switching electronic unit (120, 124) which can be opened, in the non-passing state, and closed, in the passing state, in a controlled way to switch the current flowing in the arm in which it is located is provided in each switch, - in normal mode the control unit controls the switching of the controllable power switching electronic units (120, 124) from the passing state to the non-passing state and vice versa at freely chosen times to rectify the three-phase voltage, the switching frequency of the controllable power electronic units (120, 124) being higher than at least twenty times the fundamental frequency of the three-phase voltage, and - in emergency mode, the AC powered emergency auxiliary loads are connected to the input terminals of the charger through a three-phase medium voltage auxiliary network, and - the control unit controls switching of the electronic units from the passing state to the non-passing state and vice versa at times which are freely determined to produce an auxiliary three-phase voltage on the auxiliary network enabling the emergency auxiliary loads to operate, this auxiliary three-phase voltage being produced from the energy stored in the electrical energy storage device. • three input terminals each connected to one of the phases of the three-phase voltage, • two output terminals (106, 108) connected to the electrical energy storage device to which the rectified DC voltage is delivered, • three arms connected in parallel between the two output terminals, each arm comprising two controllable switches (I H, I B) connected in series through a mid-point, each mid-point being connected to a corresponding input terminal, • a unit controlling switching of the switches to rectify the three-phase voltage, - a controllable power switching electronic unit (120, 124) which can be opened, in the non-passing state, and closed, in the passing state, in a controlled way to switch the current flowing in the arm in which it is located is provided in each switch, - in normal mode the control unit controls the switching of the controllable power switching electronic units (120, 124) from the passing state to the non-passing state and vice versa at freely chosen times to rectify the three-phase voltage, the switching frequency of the controllable power electronic units (120, 124) being higher than at least twenty times the fundamental frequency of the three-phase voltage, and - in emergency mode, the AC powered emergency auxiliary loads are connected to the input terminals of the charger through a three-phase medium voltage auxiliary network, and - the control unit controls switching of the electronic units from the passing state to the non-passing state and vice versa at times which are freely determined to produce an auxiliary three-phase voltage on the auxiliary network enabling the emergency auxiliary loads to operate, this auxiliary three-phase voltage being produced from the energy stored in the electrical energy storage device.