Electrical power supply system having a DC distribution bus; a rechargeable battery module which delivers DC power to the DC distribution bus in a discharge mode, and absorbs DC power from the DC distribution bus in a recharge mode; a DC/DC converter comprising an inductor and plural switches, the DC/DC converter being connected between the DC distribution bus and the rechargeable battery module; and a heat transfer arrangement configured to transfer heat between the DC/DC converter and the rechargeable battery module. The module has an idling mode of operation in which it neither delivers nor absorbs DC power to/from DC distribution bus, wherein the converter is repeatedly switchable between (i) a ramping-up configuration in which a current is withdrawn from a source, and (ii) a freewheeling configuration in which the current from the ramping-up configuration is isolated from the source to flow in a continuous loop within the converter.