I am not sure if it is a good idea to draw a bike charger as in my sample pic no. 4 measuring some 60x40 cm on the ground as an area with amenity=charging_station and then squeeze 4 nodes man_made=charge_point + additional nodes for the lockers into it.
Due to the multitude of options I believe it would be better to develop a separate tagging structure for bicycle chargers. But before going into the details we should clarify the question of the top level tag.
If we go for
amenity=charging_station +
bicycle=only
we should do the same for amenity=device_charging_station and change that to
amenity=charging_station +
electronic_device=only
If we to not want to touch amenity=device_charging_station we should also go for amenity=bicycle_charging_station to keep tagging schemes consistant.