Bat’ used to be an old southern Dutch word for a mooring place or a quay reinforced with wood. As an example, you can still find a location called ‘Quai de la Batte’ in Liège.
In the past, sacks filled with coal were transported into the city through a water gate called the ‘Batpoort’. The men who carried these sacks on their backs became so covered in the soot that they appeared to be as black as ravens. As these men had rather hardy reputations, naughty children in Maastricht were also called 'batteraof’ (quay ravens).