Once a battery is fully charged, the charging process is automatically stopped and switched to trickle charging (buffer charging with current impulses). This feature ensures optimum performance and counteracts the self-discharge of the battery. The battery can thus remain in the device until it is used. A clearly arranged LED display shows the current program mode for each charging slot separately. Should a non-rechargeable or defective battery be inserted accidentally, this will be indicated by a flashing red LED.