The invention relates to a battery system (10) for an electric vehicle, comprising: a battery pack (5) having a positive electrode (22), a negative electrode (21), at least one battery cell (2) and a pack voltage divider (25); and at least one coupling network having a negative connection (11) and a positive connection (12), wherein the group voltage divider (25) comprises a positive group resistor (RP2) and a positive sub-group resistor (RSP2), which are connected in series with each other between the positive electrode (22) and a reference point (50), and a negative group resistor (RP1) and a negative sub-group resistor (RSP1), which are connected in series with each other between the negative electrode (21) and the reference point (50). The at least one coupling network has a coupling voltage divider (15), the coupling voltage divider comprises a positive coupling resistor (RK2) and a positive partial coupling resistor (RSK2), which are connected in series with each other between the positive connection (12) and the reference point (50), and a negative coupling resistor (RK1) and a negative partial coupling resistor (RSK1), which are connected in series with each other between the negative connection (11) and the reference point (50). The invention also relates to a method for diagnosing a battery system (10) according to the invention, wherein a positive group voltage (UP2) occurring at the positive component-group resistor (RSP2) is measured, a negative group voltage (UP1) occurring at the negative component-group resistor (RSP1) is measured, a positive coupling voltage (UK2) occurring at the positive component-coupling resistor (RSK2) is measured, a negative coupling voltage (UK1) occurring at the negative component-coupling resistor (RSK1) is measured, and the measured voltages (UP1, UP2, UK1, UP2, UK1, UP2, UK1, UK2, UK1, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1, UK2, UK1 The invention also relates to an electric vehicle comprising a battery system (10) according to the invention.