Method for battery unbalance mitigation in a voltage conversion system, said voltage conversion system including: - a first and a second battery being connected in series with each other, - a converter having a converter input and a converter output, said converter input being connected to at least one of said first and said second battery in such a way that the voltage at the converter input is either the voltage of the first battery or the voltage of the second battery or the sum of both the voltages of the first and the second battery, said converter output providing a converter output current and a converter output voltage, said converter having a maximal converter output current ( Ic (max) out), and - a voltage conversion system output, being connected to a point between said first and said second battery and to said converter output, providing a voltage conversion system output current ( Isysout), the method comprising - detecting a battery unbalance in said voltage conversion system; - applying, when battery unbalance is detected, a first charging current ( Ib 1) to said first battery and a second charging current ( Ib 2) to said second battery for restoring a charging balance of said first and said second battery, the method being characterized in that: - said detecting of battery unbalance in said voltage conversion system comprises the step of performing a comparison of said voltage conversion system output current ( Isysout) with said maximal converter output current ( Ic (max) out), - said first and second charging currents for restoring the charging balance are determined based on a period of time during which battery unbalance has been detected to be present, and based on the amplitude of the first ( Ib 1) and second ( Ib 2) charging currents which have been used for charging the first and the second battery during said period of time, and - said first and said second charging current ( Ib 1), ( Ib 2) being different from each other, wherein the one of said first ( Ib 1) and said second ( Ib 2) charging current being the highest is applied to the one of said first and said second battery having had the smallest charging current during said period of time. - a first and a second battery being connected in series with each other, - a converter having a converter input and a converter output, said converter input being connected to at least one of said first and said second battery in such a way that the voltage at the converter input is either the voltage of the first battery or the voltage of the second battery or the sum of both the voltages of the first and the second battery, said converter output providing a converter output current and a converter output voltage, said converter having a maximal converter output current ( Ic (max) out), and - a voltage conversion system output, being connected to a point between said first and said second battery and to said converter output, providing a voltage conversion system output current ( Isysout), the method comprising - detecting a battery unbalance in said voltage conversion system; - applying, when battery unbalance is detected, a first charging current ( Ib 1) to said first battery and a second charging current ( Ib 2) to said second battery for restoring a charging balance of said first and said second battery, the method being characterized in that: - said detecting of battery unbalance in said voltage conversion system comprises the step of performing a comparison of said voltage conversion system output current ( Isysout) with said maximal converter output current ( Ic (max) out), - said first and second charging currents for restoring the charging balance are determined based on a period of time during which battery unbalance has been detected to be present, and based on the amplitude of the first ( Ib 1) and second ( Ib 2) charging currents which have been used for charging the first and the second battery during said period of time, and - said first and said second charging current ( Ib 1), ( Ib 2) being different from each other, wherein the one of said first ( Ib 1) and said second ( Ib 2) charging current being the highest is applied to the one of said first and said second battery having had the smallest charging current during said period of time. - said detecting of battery unbalance in said voltage conversion system comprises the step of performing a comparison of said voltage conversion system output current ( Isysout) with said maximal converter output current ( Ic (max) out), - said first and second charging currents for restoring the charging balance are determined based on a period of time during which battery unbalance has been detected to be present, and based on the amplitude of the first ( Ib 1) and second ( Ib 2) charging currents which have been used for charging the first and the second battery during said period of time, and - said first and said second charging current ( Ib 1), ( Ib 2) being different from each other, wherein the one of said first ( Ib 1) and said second ( Ib 2) charging current being the highest is applied to the one of said first and said second battery having had the smallest charging current during said period of time.