What happens to the C3's charging mode if it loses power during charging?

If the C3 is disconnected from the mains during charging, the unit stores the mode that was in use. On reconnection to the mains, if the battery is the same type (6 V or 12 V), the unit starts automatically in the last mode used. If a different battery type is connected (6 V vs 12 V), the unit switches to standby instead. (Page 5)