A method comprising: (i) using power converters to individually regulate storing of energy in energy storage devices, wherein the energy is stored with a plurality of variable energy storage rates, so that the energy storage devices reach pre-set values substantially at a common charging end time responsive to a common reference, wherein the common reference is a reference voltage or reference current, and wherein using the power converters to individually regulate the storing of energy comprises: maintaining individually a voltage conversion ratio based on an energy storage fraction respectively for each of the energy storage devices, and the energy storage fraction being determined by a monitoring of a fuel gauge connected to the energy storage devices; and (ii) using the power converters to individually regulate depletion of the energy from the energy storage devices, wherein the energy is depleted with a plurality of variable energy depletion rates, so that the energy storage devices reach a depleted state substantially at a common discharging end time responsive to the common reference, and wherein using the power converters to individually regulate the depletion of the energy comprises: controlling individually the voltage conversion ratio based on the energy storage fraction respectively for each of the energy storage devices, and updating at least one of the energy storage fraction and the common reference responsive to the monitoring of the fuel gauge connected to the energy storage devices, wherein each of the power converters comprises a controller, and wherein the energy storage fraction used to regulate the storing of energy and the depletion of the energy from the energy storage devices being further determined by the controller analyzing information stored in a memory and based on monitoring data provided by the fuel gauge, the memory storing information comprising: a) the energy storage capacity with respect to the energy storage devices, b) monitoring and measuring of energy storage with respect to the energy storage devices, and c) depletion of energy storage with respect to the energy storage devices. (i) using power converters to individually regulate storing of energy in energy storage devices, wherein the energy is stored with a plurality of variable energy storage rates, so that the energy storage devices reach pre-set values substantially at a common charging end time responsive to a common reference, wherein the common reference is a reference voltage or reference current, and wherein using the power converters to individually regulate the storing of energy comprises: maintaining individually a voltage conversion ratio based on an energy storage fraction respectively for each of the energy storage devices, and the energy storage fraction being determined by a monitoring of a fuel gauge connected to the energy storage devices; and (ii) using the power converters to individually regulate depletion of the energy from the energy storage devices, wherein the energy is depleted with a plurality of variable energy depletion rates, so that the energy storage devices reach a depleted state substantially at a common discharging end time responsive to the common reference, and wherein using the power converters to individually regulate the depletion of the energy comprises: controlling individually the voltage conversion ratio based on the energy storage fraction respectively for each of the energy storage devices, and updating at least one of the energy storage fraction and the common reference responsive to the monitoring of the fuel gauge connected to the energy storage devices, wherein each of the power converters comprises a controller, and wherein the energy storage fraction used to regulate the storing of energy and the depletion of the energy from the energy storage devices being further determined by the controller analyzing information stored in a memory and based on monitoring data provided by the fuel gauge, the memory storing information comprising: a) the energy storage capacity with respect to the energy storage devices, b) monitoring and measuring of energy storage with respect to the energy storage devices, and c) depletion of energy storage with respect to the energy storage devices. a) the energy storage capacity with respect to the energy storage devices, b) monitoring and measuring of energy storage with respect to the energy storage devices, and c) depletion of energy storage with respect to the energy storage devices.