An energy control unit for use in a hybrid vehicle having an electric motor operable to provide a source of drive power to the hybrid vehicle, an energy storage unit operatively coupled to the electric motor to provide a first source of energy to the electrical motor, and a prime mover operatively coupled to the electric motor to provide a second source of energy to the electric motor, characterized in that the energy control unit configured to communicate with the energy storage unit and a generator in the hybrid vehicle and is operable to control charging of the energy storage unit via a generator coupled to the prime mover based on an energy level of the hybrid vehicle and a predicted mechanical potential energy of the hybrid vehicle over a future route to be traversed by the vehicle such that the energy level of the hybrid vehicle is maintained substantially at a desired magnitude, the energy level of the hybrid vehicle being a function of at least: (i) mechanical kinetic energy of the hybrid vehicle; (ii) mechanical potential energy of the hybrid vehicle, derived from the hybrid vehicle weight or mass; and (iii) potential energy of the energy storage unit, wherein the energy control unit comprises a terrain prediction unit configured to estimate grade angles of surfaces on which the hybrid vehicle will travel over the future route and lengths of the surfaces and predict the mechanical potential energy of the hybrid vehicle based thereon, and wherein the energy control unit further comprises a storage device storing a base estimation of the weight or mass of the hybrid vehicle and the energy control unit is configured to communicate with at least one sensor in the hybrid vehicle configured to estimate a weight or mass of fuel and/or a weight or mass of a passenger and the energy control unit is configured to receive the estimated weight or mass of fuel and/or a weight or mass of a passenger from the at least one sensor and the energy control unit is operable to estimate the hybrid vehicle weight or mass by aggregating the stored base estimation of the weight or mass of the hybrid vehicle with at least the received estimate of weight or mass of fuel and/or the weight or mass of a passenger from the at least one sensor. the energy control unit configured to communicate with the energy storage unit and a generator in the hybrid vehicle and is operable to control charging of the energy storage unit via a generator coupled to the prime mover based on an energy level of the hybrid vehicle and a predicted mechanical potential energy of the hybrid vehicle over a future route to be traversed by the vehicle such that the energy level of the hybrid vehicle is maintained substantially at a desired magnitude, the energy level of the hybrid vehicle being a function of at least: (i) mechanical kinetic energy of the hybrid vehicle; (ii) mechanical potential energy of the hybrid vehicle, derived from the hybrid vehicle weight or mass; and (iii) potential energy of the energy storage unit, wherein the energy control unit comprises a terrain prediction unit configured to estimate grade angles of surfaces on which the hybrid vehicle will travel over the future route and lengths of the surfaces and predict the mechanical potential energy of the hybrid vehicle based thereon, and (i) mechanical kinetic energy of the hybrid vehicle; (ii) mechanical potential energy of the hybrid vehicle, derived from the hybrid vehicle weight or mass; and (iii) potential energy of the energy storage unit, wherein the energy control unit further comprises a storage device storing a base estimation of the weight or mass of the hybrid vehicle and the energy control unit is configured to communicate with at least one sensor in the hybrid vehicle configured to estimate a weight or mass of fuel and/or a weight or mass of a passenger and the energy control unit is configured to receive the estimated weight or mass of fuel and/or a weight or mass of a passenger from the at least one sensor and the energy control unit is operable to estimate the hybrid vehicle weight or mass by aggregating the stored base estimation of the weight or mass of the hybrid vehicle with at least the received estimate of weight or mass of fuel and/or the weight or mass of a passenger from the at least one sensor.