An electrical circuit for a motor vehicle having electrical equipment and an internal combustion engine , the electrical circuit comprising: - a first electrical battery (B1), connected to at least some of said electrical equipment via a first controlled switch (K1), - a second electrical battery (B2; B2'), connected to at least some of said electrical equipment via a second controlled switch (K2), 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 (K1) to adopt an open state and the second switch (K2) to adopt a closed state when the motor vehicle is parked for a long time, and to - control the first switch (K1) 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 (U1) of the first battery (B1), 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 (T1), and data representative of a charge level of the first battery (SOC1), - on the basis of said data, compare the charge level of the first battery (SOC1) with a start-up charge level (SOC1 dem ) for which the first battery (B1), at said temperature (T1), is capable of starting up the internal combustion engine , and - when this comparison shows that the charge level of the first battery (SOC1) 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 (B1), connected to at least some of said electrical equipment via a first controlled switch (K1), - a second electrical battery (B2; B2'), connected to at least some of said electrical equipment via a second controlled switch (K2), 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 (K1) to adopt an open state and the second switch (K2) to adopt a closed state when the motor vehicle is parked for a long time, and to - control the first switch (K1) 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 (U1) of the first battery (B1), and in that - acquire data representative of a temperature of the first battery (T1), and data representative of a charge level of the first battery (SOC1), - on the basis of said data, compare the charge level of the first battery (SOC1) with a start-up charge level (SOC1 dem ) for which the first battery (B1), at said temperature (T1), is capable of starting up the internal combustion engine , and - when this comparison shows that the charge level of the first battery (SOC1) 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. <EOS>