BATTERY CHARGER

A battery charging system is proposed which has an AC generator (10), a voltage regulator (20) and a charge monitoring device for indicating defects. The latter is provided with a signal transmitter (82) for detecting the switching state of the voltage regulator, a first threshold-value stage (67) for detecting a minimum value of the generator voltage, and a second threshold-value stage (69) for detecting a voltage which is a specific amount above the required control value, at a sensing point in the system. One input of the first threshold-value stage (67) is connected to a fault detection connection (D+), which is decoupled from the battery voltage, on the excitation system (12, 14) of the generator. The second threshold-value stage (69) is connected on the input side to a sensing point which is influenced by the battery voltage. This has the advantage that the first threshold-value stage (67) can detect and evaluate the generator voltage without being influenced by the charge state of the battery and without being corrupted, and the second threshold-value stage can detect and evaluate the charge state of the battery without being corrupted.