Method for determining the state of charge of a rechargeable battery or a parameter physically related thereto, in particular a residual charge quantity Q contained in the battery, wherein the method comprises the following steps: (a) creating a voltage-controlled dynamic mathematical battery model for the battery or a specified battery type for the battery, (i) which links a state of charge of the battery SOC mod or the parameter physically related thereto to a battery current I mod, and (ii) which defines a voltage U mess measured between the two poles of the battery as a function of a sum of an open circuit voltage U 0 of the battery and an overvoltage η, (iii) wherein the open circuit voltage U 0 is dependent at least on the residual charge quantity Q or the parameter physically related thereto and the overvoltage η is dependent at least on the battery current I mod; and (iv) wherein the voltage-controlled dynamic mathematical battery model consists of or is developed from an implicit system of equations comprising the following equations: dSOC mod d t = I mod C N U mess = U 0 SOC mod T mess t + η I mod SOC mod T mess t where C N denotes a specified nominal capacity of the battery, T mess denotes a measured temperature of the battery and t denotes the time, wherein the open circuit voltage U 0 necessarily exhibits a dependence on the state of charge SOC mod, while the dependence on the measured temperature T mess and the time t is optional, and wherein the overvoltage η necessarily exhibits a dependence on the battery current I mod, while the dependence on the state of charge SOC mod and the time t is optional; (b) parameterizing the voltage-controlled dynamic mathematical battery model for the battery or the specified battery type; and (c) determining an approximate value SOC mod for the actual state of charge SOC of the battery or the parameter physically related thereto by measuring the battery voltage U mess and calculating the approximate value SOC mod using the parameterized voltage-controlled dynamic mathematical battery model. (a) creating a voltage-controlled dynamic mathematical battery model for the battery or a specified battery type for the battery, (i) which links a state of charge of the battery SOC mod or the parameter physically related thereto to a battery current I mod, and (ii) which defines a voltage U mess measured between the two poles of the battery as a function of a sum of an open circuit voltage U 0 of the battery and an overvoltage η, (iii) wherein the open circuit voltage U 0 is dependent at least on the residual charge quantity Q or the parameter physically related thereto and the overvoltage η is dependent at least on the battery current I mod; and (iv) wherein the voltage-controlled dynamic mathematical battery model consists of or is developed from an implicit system of equations comprising the following equations: dSOC mod d t = I mod C N U mess = U 0 SOC mod T mess t + η I mod SOC mod T mess t where C N denotes a specified nominal capacity of the battery, T mess denotes a measured temperature of the battery and t denotes the time, wherein the open circuit voltage U 0 necessarily exhibits a dependence on the state of charge SOC mod, while the dependence on the measured temperature T mess and the time t is optional, and wherein the overvoltage η necessarily exhibits a dependence on the battery current I mod, while the dependence on the state of charge SOC mod and the time t is optional; (i) which links a state of charge of the battery SOC mod or the parameter physically related thereto to a battery current I mod, and (ii) which defines a voltage U mess measured between the two poles of the battery as a function of a sum of an open circuit voltage U 0 of the battery and an overvoltage η, (iii) wherein the open circuit voltage U 0 is dependent at least on the residual charge quantity Q or the parameter physically related thereto and the overvoltage η is dependent at least on the battery current I mod; and (iv) wherein the voltage-controlled dynamic mathematical battery model consists of or is developed from an implicit system of equations comprising the following equations: dSOC mod d t = I mod C N U mess = U 0 SOC mod T mess t + η I mod SOC mod T mess t dSOC mod d t = I mod C N U mess = U 0 SOC mod T mess t + η I mod SOC mod T mess t (b) parameterizing the voltage-controlled dynamic mathematical battery model for the battery or the specified battery type; and (c) determining an approximate value SOC mod for the actual state of charge SOC of the battery or the parameter physically related thereto by measuring the battery voltage U mess and calculating the approximate value SOC mod using the parameterized voltage-controlled dynamic mathematical battery model.