An electrical circuit for a motor vehicle having electrical equipment (4, 5, 6) and an internal combustion engine, the electrical circuit comprising: - a first electrical battery, connected to at least some of said electrical equipment (4, 5, 6) via a first controlled switch, - a second electrical battery (B2; B2'), connected to at least some of said electrical equipment (4, 5, 6) via a second controlled switch, and - an electronic control unit capable of controlling the first and second controlled switches (K1, K2), characterized in that: - the control unit is programmed to: - control the first switch to adopt an open state and the second switch to adopt a closed state when the motor vehicle is parked for a long time, and to - control the first switch to adopt a closed state during the start-up phase of the internal combustion engine, in that - at the same charge level and within at least one given range of charge levels, the open-circuit voltage (U2; U2') of the second battery (B2; B2') is higher than the open-circuit voltage of the first battery, and in that the control unit is programmed to, when the vehicle is parked for a long time: - acquire data representative of a temperature of the first battery, and data representative of a charge level of the first battery, - on the basis of said data, compare the charge level of the first battery with a start-up charge level (SOC1 dem) for which the first battery, at said temperature, is capable of starting up the internal combustion engine, and - when this comparison shows that the charge level of the first battery is lower than said start-up charge level (SOC1 dem), to control both the first and second controlled switches (K1, K2) to adopt their closed states. - a first electrical battery, connected to at least some of said electrical equipment (4, 5, 6) via a first controlled switch, - a second electrical battery (B2; B2'), connected to at least some of said electrical equipment (4, 5, 6) via a second controlled switch, and - an electronic control unit capable of controlling the first and second controlled switches (K1, K2), - the control unit is programmed to: - control the first switch to adopt an open state and the second switch to adopt a closed state when the motor vehicle is parked for a long time, and to - control the first switch to adopt a closed state during the start-up phase of the internal combustion engine, in that - at the same charge level and within at least one given range of charge levels, the open-circuit voltage (U2; U2') of the second battery (B2; B2') is higher than the open-circuit voltage of the first battery, and in that - acquire data representative of a temperature of the first battery, and data representative of a charge level of the first battery, - on the basis of said data, compare the charge level of the first battery with a start-up charge level (SOC1 dem) for which the first battery, at said temperature, is capable of starting up the internal combustion engine, and - when this comparison shows that the charge level of the first battery is lower than said start-up charge level (SOC1 dem), to control both the first and second controlled switches (K1, K2) to adopt their closed states.