| CPC G01R 31/387 (2019.01) [H02J 7/0048 (2020.01); H02J 7/007182 (2020.01)] | 13 Claims |

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1. A method for determining the capacity of an electrical energy storage unit (2) within an electrical energy storage system (1) that includes a plurality of electrical energy storage units (2), a sensor, and at least one switch (3), which is designed to switch the electrical energy storage unit (2) whose capacity is being determined electrically out of a current flow path (5) of the electrical energy storage system (1) and/or to switch said electrical energy storage unit (2) electrically into the current flow path (5), wherein the sensor is configured to detect a voltage of the electrical energy storage unit (2), said method comprising the following steps:
a) switching, by the switch (3), the electrical energy storage unit (2) out of the current flow path (5) of the electrical energy storage system (1);
b) determining, by the sensor, a first voltage value of a terminal voltage of the electrical energy storage unit (2);
c) switching, by the switch (3), the electrical energy storage unit (2) into the current flow path (5) of the electrical energy storage system (1);
d) charging and/or discharging the electrical energy storage unit (2) with a predefined first quantity of charge and/or up to a predefined first state of charge and/or up to a predefined first voltage level;
e) switching, by the switch (3), the electrical energy storage unit (2) out of the current flow path (5) of the electrical energy storage system (1) again
f) determining, by the sensor, a second voltage value of the terminal voltage of the electrical energy storage unit (2); and
g) determining, by an electronic control unit, the capacity of the electrical energy storage unit (2) in dependence on the first voltage value and the second voltage value.
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