How to prevent AC500 to deplete completely

When I charge my PHEV car with the AC500 + B300s, quite often the unit depletes completely and switches AC Off.
Sometimes it throws a 054 D-Bat Drained alarm, but not every time.
Is there a way to prevent the complete discharge?

@southside There is no way to prevent this from happening if the unit is discharging without being connected to AC input. The battery will continue to discharge until it is depleted. We recommend charging the unit promptly after it is fully discharged to avoid this issue.