A system comprising: a first energy storage device; a second energy storage device coupled to the first energy storage device and charged via a charging current from the first energy storage device; a power controller comprising a processor, and a converter coupled to the processor and directed via switch control signals from the processor; and an output terminal via which power is provided to a load of the system, wherein the converter is disposed between the first energy storage device and the output terminal and between the first and second energy storage devices (504, 506); wherein: the first and second energy storage devices (504, 506) have first and second power densities respectively, wherein the second power density is higher than the first power density; the converter is configured to control a level of the charging current in accordance with the switch control signals; characterised in that: the power controller comprises a memory coupled to the processor on which charging current instructions are stored, wherein the charging current instructions are executed by the processor to cause the processor to generate the switch control signals such that the level of the charging current is regulated; and the converter is configured as a unidirectional DC/DC converter. a first energy storage device; a second energy storage device coupled to the first energy storage device and charged via a charging current from the first energy storage device; a power controller comprising a processor, and a converter coupled to the processor and directed via switch control signals from the processor; and an output terminal via which power is provided to a load of the system, wherein the converter is disposed between the first energy storage device and the output terminal and between the first and second energy storage devices (504, 506); wherein: the first and second energy storage devices (504, 506) have first and second power densities respectively, wherein the second power density is higher than the first power density; the converter is configured to control a level of the charging current in accordance with the switch control signals; characterised in that: the power controller comprises a memory coupled to the processor on which charging current instructions are stored, wherein the charging current instructions are executed by the processor to cause the processor to generate the switch control signals such that the level of the charging current is regulated; and the converter is configured as a unidirectional DC/DC converter. the first and second energy storage devices (504, 506) have first and second power densities respectively, wherein the second power density is higher than the first power density; the converter is configured to control a level of the charging current in accordance with the switch control signals; characterised in that: the power controller comprises a memory coupled to the processor on which charging current instructions are stored, wherein the charging current instructions are executed by the processor to cause the processor to generate the switch control signals such that the level of the charging current is regulated; and the converter is configured as a unidirectional DC/DC converter. the power controller comprises a memory coupled to the processor on which charging current instructions are stored, wherein the charging current instructions are executed by the processor to cause the processor to generate the switch control signals such that the level of the charging current is regulated; and the converter is configured as a unidirectional DC/DC converter.