A system comprising: an AC electrical power source; a DC electrical power source; an energy storage device configured to store DC electrical power and provide DC electrical power to a DC load; a regulator operatively connected to the energy storage device and configured to convert AC electrical power, from the AC electrical power source, to DC electrical power, or to condition DC electrical power, from the DC electrical power source, and to provide the DC electrical power to the energy storage device and/or to the DC load; and a controller in communication with the energy storage device and the regulator, and operable to: store at least one of a determined profile or map of recharge resistance value versus the state of charge of the energy storage device; determine an optimal partial state-of-charge (PSOC) window of operation defined by upper and lower state of charge levels of the energy storage device, based on the at least one of the profile or the map, which at least one of conserves fuel or other energy used by the AC electrical power source or which conserves energy produced and/or stored by the DC electrical power source; cyclically turn at least one of the AC electrical power source or the DC electrical power source on and off based on the determined partial state-of-charge (PSOC) window of operation so as to cyclically charge the energy storage device to the upper state of charge level and discharge the energy storage device to the lower state of charge level; and periodically turn at least one of the AC electrical power source or the DC electrical power source on and off so as to cyclically charge the energy storage device to a 100% state of charge level to reset the chemistry and/or a battery management system of the energy storage device. an AC electrical power source; a DC electrical power source; an energy storage device configured to store DC electrical power and provide DC electrical power to a DC load; a regulator operatively connected to the energy storage device and configured to convert AC electrical power, from the AC electrical power source, to DC electrical power, or to condition DC electrical power, from the DC electrical power source, and to provide the DC electrical power to the energy storage device and/or to the DC load; and a controller in communication with the energy storage device and the regulator, and operable to: store at least one of a determined profile or map of recharge resistance value versus the state of charge of the energy storage device; determine an optimal partial state-of-charge (PSOC) window of operation defined by upper and lower state of charge levels of the energy storage device, based on the at least one of the profile or the map, which at least one of conserves fuel or other energy used by the AC electrical power source or which conserves energy produced and/or stored by the DC electrical power source; cyclically turn at least one of the AC electrical power source or the DC electrical power source on and off based on the determined partial state-of-charge (PSOC) window of operation so as to cyclically charge the energy storage device to the upper state of charge level and discharge the energy storage device to the lower state of charge level; and periodically turn at least one of the AC electrical power source or the DC electrical power source on and off so as to cyclically charge the energy storage device to a 100% state of charge level to reset the chemistry and/or a battery management system of the energy storage device. store at least one of a determined profile or map of recharge resistance value versus the state of charge of the energy storage device; determine an optimal partial state-of-charge (PSOC) window of operation defined by upper and lower state of charge levels of the energy storage device, based on the at least one of the profile or the map, which at least one of conserves fuel or other energy used by the AC electrical power source or which conserves energy produced and/or stored by the DC electrical power source; cyclically turn at least one of the AC electrical power source or the DC electrical power source on and off based on the determined partial state-of-charge (PSOC) window of operation so as to cyclically charge the energy storage device to the upper state of charge level and discharge the energy storage device to the lower state of charge level; and periodically turn at least one of the AC electrical power source or the DC electrical power source on and off so as to cyclically charge the energy storage device to a 100% state of charge level to reset the chemistry and/or a battery management system of the energy storage device.