An arrangement for charging batteries, the arrangement comprising: cell groups that include one or more cells, a battery pack that comprises two or more cell groups connected in series, monitoring units for the cell groups, wherein each monitoring unit is arranged to manage the voltage ( U B ) of a cell group by controlling a part, i.e. a bypass current ( I S ) of a charging current to pass through a bypass circuit of the monitoring unit bypassing the cell group when the voltage ( U B ) of the cell group reaches a reference voltage, and wherein each monitoring unit comprises means for determining control data ( ctrl ) to be transmitted to a charger , and the charger arranged to charge the battery pack and comprising means for charging the battery pack in response to control data ( ctrl ) determined by any monitoring unit , wherein each monitoring unit comprises an amplifier (4.1), an inverting input of each such amplifier (4.1) is coupled to receive, via a first summing resistor (4.4) and a second summing resistor (4.5), a sum of an actual cell voltage value ( U B,0 ) of the respective cell group and a voltage ( U BIS,0 ) proportional to the voltage ( U B ) of the respective cell group and the respective bypass current ( I S ) , a non-inverting input of each such amplifier is coupled to receive the reference voltage ( U REF ), each monitoring unit is arranged to allow the voltage ( U B ) of the cell group to increase in response to an increase in the bypass current ( I S ) of the bypass circuit of the monitoring unit , the means for determining control data are arranged to determine the control data ( ctrl ) in response to the voltage ( U B ) of the cell group and the charger comprises means for changing a charging voltage in response to the control data (ctrl) determined by any monitoring unit . cell groups that include one or more cells, a battery pack that comprises two or more cell groups connected in series, monitoring units for the cell groups, wherein each monitoring unit is arranged to manage the voltage ( U B ) of a cell group by controlling a part, i.e. a bypass current ( I S ) of a charging current to pass through a bypass circuit of the monitoring unit bypassing the cell group when the voltage ( U B ) of the cell group reaches a reference voltage, and wherein each monitoring unit comprises means for determining control data ( ctrl ) to be transmitted to a charger , and the charger arranged to charge the battery pack and comprising means for charging the battery pack in response to control data ( ctrl ) determined by any monitoring unit , wherein each monitoring unit comprises an amplifier (4.1), an inverting input of each such amplifier (4.1) is coupled to receive, via a first summing resistor (4.4) and a second summing resistor (4.5), a sum of an actual cell voltage value ( U B,0 ) of the respective cell group and a voltage ( U BIS,0 ) proportional to the voltage ( U B ) of the respective cell group and the respective bypass current ( I S ) , a non-inverting input of each such amplifier is coupled to receive the reference voltage ( U REF ), each monitoring unit is arranged to allow the voltage ( U B ) of the cell group to increase in response to an increase in the bypass current ( I S ) of the bypass circuit of the monitoring unit , the means for determining control data are arranged to determine the control data ( ctrl ) in response to the voltage ( U B ) of the cell group and the charger comprises means for changing a charging voltage in response to the control data (ctrl) determined by any monitoring unit . <EOS>