A method for controlling a power management system in a vehicle operated by a combustion engine , wherein said system comprises a control unit , said method comprising: - supplying electric energy to a start device for said combustion engine by means of a start battery unit ; - supplying electric energy to a number of electric consumers in the vehicle including components which are crucial for allowing starting of said combustion engine , by means of a second battery unit ; and - charging said second battery unit during operation of the combustion engine by means of an alternator which is associated with said combustion engine ; - checking, before starting of the combustion engine by means of said start device , whether the state of charge (SOC 1 ) of said second battery unit is lower than a predetermined value, and, if this is the case, - accepting an input signal for actuation of said start device if the state of charge (SOC 2 ) of said start battery unit is higher than a predetermined value; and - during actuation of said start device , supplying electric energy to said crucial components from the start battery unit by means of a battery charging unit which is also configured for charging the start battery unit during operation of the vehicle with electric energy from said second battery unit , said battery charging unit being reversed for supplying electric energy from said start battery unit to said crucial components ; characterized in that said method further comprises: - maintaining the voltage of the output of the battery charging unit , which voltage is delivered to said crucial components and to said second battery unit , below a charging acceptance voltage of said second battery unit , under which said second battery unit can not be charged; and - thereby inhibiting charging of said second battery unit during actuation of the start device while supplying electric energy to said crucial components . - supplying electric energy to a start device for said combustion engine by means of a start battery unit ; - supplying electric energy to a number of electric consumers in the vehicle including components which are crucial for allowing starting of said combustion engine , by means of a second battery unit ; and - charging said second battery unit during operation of the combustion engine by means of an alternator which is associated with said combustion engine ; - checking, before starting of the combustion engine by means of said start device , whether the state of charge (SOC 1 ) of said second battery unit is lower than a predetermined value, and, if this is the case, - accepting an input signal for actuation of said start device if the state of charge (SOC 2 ) of said start battery unit is higher than a predetermined value; and - during actuation of said start device , supplying electric energy to said crucial components from the start battery unit by means of a battery charging unit which is also configured for charging the start battery unit during operation of the vehicle with electric energy from said second battery unit , said battery charging unit being reversed for supplying electric energy from said start battery unit to said crucial components ; - maintaining the voltage of the output of the battery charging unit , which voltage is delivered to said crucial components and to said second battery unit , below a charging acceptance voltage of said second battery unit , under which said second battery unit can not be charged; and - thereby inhibiting charging of said second battery unit during actuation of the start device while supplying electric energy to said crucial components . <EOS>